The only advice I'd give here is to say that you'll want to focus more on the Renew casts than PoH. In 10-normal a renew is easily enough to keep infest under control, and by allowing you to stay mobile it will make your life far simpler.
LK-10-normal is mostly about being in the right place at the right time, so focusing on your instants makes that easier. That's not to say that PoH isn't in principle better, it is since it allows you to deal with infest in fewer GCDs - however if infest is coinciding with valks or defile (as it often will) then keeping hots up will make your life far far simpler.
Oh and if you have to do the disease then I advise you to bind 'cure disease' somewhere rather than use abolish.
The danger with abolish is that if you don't have perfect control over the disease, abolish will make your life even worse. Consider the following scenario:
1: Disease targets a dps
2: Dps runs to mobs
3: Abolish on Dps
4: Disease jumps to offtank
5: Abolish on OT, dps is still stood around like a lemon
6: Disease jumps back to DPS
7: DPS runs to pack
8: Abolish still ticking - uh oh - here comes trouble.
If you don't think that kind of thing happens, well, trust me it does.
I like my SoL but it proccs enough with just one point. I only used Inner Focus with Divine Hymn - can't say I miss it... I'd rather have the point in SoL or Body and Soul. You really should have BS - it's great for people with disease that need to get to the tank in time...
And, just my personal oppinion - while I understand you want to play as holy, and I am sure you'd do a great job at it etc, I would personally not go without a disc priest for that fight. Yes it is doable and it's all nice and cool, but it's a bit like writing with your left hand when you should really probably write with your right one... I am a proud holy priest, but I spec disc for that fight when there are no other priests in the raid to do it because it is simply playing it safer in a fight where there are enough things going around that can ruin it.
Anyway back to the holy thing - you can have all talents and a few more. You shouldn't have any of the GH enhancing ones anyway so there are enough points to go around for both PoH and Renew talents.
Oh and don't spec that atrocity of a spec someone posted above... it's horrible for pretty much anything but FH spamming, and that's not what you should be doing anyway.
but it's a bit like writing with your left hand when you should really probably write with your right one...
Hey! I resent that; I'm left handed.
While overall Disc is the safer option for LK, and I feel very similarly to Dianthe's above post (for the most part, right handed bastard) the main factor for me is likely mana. Disc (especially on LK) has access to basically infinite mana.
The last time I tried LK 10 hc (I haven't raided in many weeks) I was disc and my partner was a resto druid. I had to heal the tanks so much that my output felt a little gimped as disc, but as holy I pretty positive I wouldn't have been able to keep up the blue bar.
That said, Holy does have a few advantages for LK hc imo. The higher output, a tank cooldown on a 1 (not 2.4) min cd, an on demand sprint for any raid member, and vastly superior aoe healing inside frostmourne.
Kelesti's spec is excellent for Normal LK-10 (though I'd probably go with 1/2 SoL over IF). You shouldn't have difficulty healing Normal LK-10 with that healing comp, typically just using a CoH on the largest cluster (typically ranged in P1, and probably melee in P2) will counter Infest. Though, sometimes, you may have to use a PoH if the Infest lines up poorly with a Defile.
In fact, to those who say spec Disc, I disagree, in that I think Holy is superior to Disc for Normal, particularly if you're 3-healing it. The simple reason is that I could counter Infest in most cases with a CoH and possibly a follow up FH, where Disc takes several more GCDs to effectively counter it. I would rarely have to use PoH, especially if you're healing with a shaman, as their CHs will typically fill in where your CoH misses. Holy also has an easier time healing the transition phases. And, of course, I find B&S and GS to be both very useful, B&S for helping with Defile placement and kiting Vile Spirits, and GS because of the short CD.
And a bit off-topic, but related: Disc does become clearly superior for HLK because CoH isn't strong enough, timing PoHs perfectly can become very difficult with all the additional moving in P1, and mana is also more of a concern. Since most comps depend on 2-healing (though, with 30%, 3-healing is doable with a good comp and gear), you have to depend on the other healer to manage the tank and PWS then because the most effective way to counter Infest since timing PoHs just isn't always feasible. I would consider running Holy if 3-healing it, but Holy for 2-healing is just adding a level of difficulty that doesn't need to be there.
If you're talking about 10 normal, really it doesn't matter all that much whether you are holy or disc. Disc makes dealing with infest easier, and Disc also has far better regen mechanics, especially specific to this fight (the ability to get mass rapture procs). Empowered Renew 3/3 should be in every holy spec; there is no reason to take this, even on H LK, when you won't be renewing as often as normal. The direct heal portion procs holy concentration and surge of light, and it adds a lot of throughput to renew. You will at least be keeping renew on tanks and melee that are aggroing ghouls. Serendipity and Body and Soul are both situational and option depending on playstyle.
The problem with holy on this fight (TBH, it really is only even an issue on 25 heroic) is the fight is so long and healing intensive that regen becomes a real issue. I personally favor going to an 18/53 spec, such as this for H LK 25. The difference mana efficiency with and without Mental Agility is just massive. Test of Faith for LK is very weak, because the whole point of healing the fight correctly is that noone ever drops low enough in health to use Test of Faith. If anyone drops that low, they will likely die to infest. If you want to have Body and Soul in addition to Serendipity, you can still do it with an 18/53 spec by dropping 2 points out of Blessed Resilience. Yes, it's 2% output, but with overheal percentages of 50%+, typically alot of that output is wasted.
That said, most of my preference for a Mental Agility spec has to do with the fact that H LK 25 is the primary version of this fight I spend time on, and our healing/replenishment situation is often not ideal. (We often have no ret pallies, which means you have to rely on spriests casting Mind Blast for replen and also often do not have any Mana Tides). If I was always in a group with 2 resto shamans and a raid with 3 ret pallies, I probably wouldn't go 18/53.
If you want to use a standard 13/58 spec, here is what I favor.
As far as being holy vs being disc, on normal mode, it really doesn't matter. If you are doing 10 LK heroic or working on it, pretty much, be disc. Unless your DPS is incredible, you are going to need to 2 heal this fight to meet the enrage. The most common combination is a Disc Priest and Holy Pally to trivialize infest and tank healing. The only time there is a lot of raid damage outside infest is P3 Frostmourne Room (this is what you glyph Holy Nova for). I think you would have a hard time doing this fight without a Disc Priest on 10 HM. You might be able to do it without a pally (I have 2 healed it with a resto druid before) but it becomes a lot harder. I don't think you can 2 heal it with a holy priest and disc priest, just because the non disc healer has to be on the tanks, and holy doesn't really have the throughput or lasting power for tank healing to handle it.
25 Heroic, both specs are viable. You want 1 (maybe 2 depending on strategy) disc priests. If it's 1 Disc, they will keep 15-20 people shielded. The rest of the healers have to heal off the rest of the infest. Holy priests are the best healers at doing this, because of the ability to pre-cast a PoH on the 1 group the disc is not shielding, followed by a CoH to clear more infests outside that group. The only thing for 25 heroic is, you want to have Serendipity, because you have lulls between infests where you can easily stack it up to be ready for the infest.