I have 11 level 85s on one server and some profession slots free. I wonder what will be good professions to have multiple of, considering I use them solely to make gold. I now have 2 Ench, 2 Mine, 2 JC, 1 Tailor, 1 Inscr, 1 LW, 5 Alch, 1 BS, 1 Eng and 2 Herb. This leaves me with 4 free slots, but I could get 2 more by dropping 1 mining and 1 herbalism (I rerolled my druid as Min/Herb, so the other chars don't really need it any more).
I was thinking of getting 2 more alchemists (the others with free slots already have alchemy) and 1 scribe for milling, but what other profs would be good to have multiple of?
I found that giving out some gathering profs to my mains is the better way to fill up prof slots. It's a bit annoying having to log that particular toon you otherwise never use when you want 5-10 ore or so, and on a main i almost always take the 10s needed if i see a giant ore vein.
Otherwise Alchemy doubles is definitively the way i would go, extra transmute a day is always easy money and extra proc type is good too.
1) Alchemists - 1 potion, 1 flask, and as many transmute as you can
2) Engineers - 1 Goblin and 1 Gnome (for the new mounts and maybe more stuff?)
3) Jewelcrafters - the more you have the more times you can do the daily quest and get new recipes faster. Could be very confusing though to remember which JC has which recipe unless you devote each JC to a colored gem
4) Tailoring - Long cooldown on specialty cloth.
Pretty much every other profession has no real need to have more than one of unless you want multiple gathers and then leave them logged out near the best gathering spots.
Alchemy - so you can get multiple specializations. Also multiple transmute cooldowns.
JC - allows you to get more cuts more quickly by doing more dailies.
Tailoring - multiple dreamcloth cooldowns.
Engineering - some specialization things, although the differences between goblin/gnomish are pretty small.