Ok lets recap shall we:
1) Paragraphs, they are your best friend whenever you want answers. Most people tend to get bored when reading a huge bunch of sentences clogged up.
2) Read read READ the %@&"ing stickies
3) Im pretty sure on Cap's sticky theres a question 90% if not 100% exactly the same as the one you did.
4) If you want to be a tankadin then go for it, many guilds like to have at least one tankadin for those tricky situations in raids, and personally I love them because the give me "teh goodz goodz salv!!" wich helps people not die (of course with all the other helpful auras and buffs, but salv = me <3).
Probably, MOST PROBABLY people will want you to go holy, for healing in raids, since paladins are the best single target healers there are, very fond for MT healing.
5) Dont let anyone tell you what to do (unless you are doing something completely retarded like... I dont know 2 handed holy spec tanking with blessing of salvation... LoL) specially if you dont ask for help. Do whatever you feel like doing, and be happy doing it.