I don't think you can go wrong either way as long as you primarily go strength. Haste and Mastery are both pretty valuable at 463.
A lot of Paladins do run Sacred shield and it's nice, but a 3 stack Selfless Flash of Light hits like a Lay on Hands. With so much spike damage and oh shit moments I found selfless better. You can try both, it really does come down to preference. If you're running with a good healer you would be fine with shield.
I liked Light's Hammer for prot, but as ret, there's a lot of single target time on bosses so Execution pulls ahead for me. Trash melts if you have the right classes in your group and most time is spent on bosses.
It's definitely stressful the first time around. But after I did my first tank I preferred tanking because I felt I had more control over the success of the group lol.
GL though. I wouldn't spend too much time trying to figure out the best gems/talents though, I went into CMs with my warrior without knowing anything and did just fine. The most important part is understanding the mechanics and knowing the pace of the dungeon.