#1-instant ocean is fine.. The reef crystals is simply a bit higher in calcium and trace elements,etc... You can switch if you want but you might not even notice the difference except level changes.. I think the price is basically the same so why not.. I use it and am very happy with it.
#2-Dosing (cal/alk,etc..) is simply done because your tank is consuming that faster than your water changes are replenishing it.. This is more of an issue with stony corals,etc... as they need more to grow their hard bodies,etc..Many can get by on just water changes alone keeping the levels in check (and consistent) and others with tons of corals,etc.. must dose everyday or the main parameters would be fluctuating all over the place and constantly being too low thus inhibiting growth,etc..
#3-Beginning corals.. mushrooms/zoas/softies/some lps (frogspawn/hammer/torch/favia/favites),etc.. I highly recommend staying away from SPS corals until you know exactly what you are doing and maintain a pristine/stable tank.
I'd suggest heading over to live aquaria site and browsing through their stock.. I believe they have a whole section of "beginner/easy" corals there..
