You are seriously going to have fun playing piano, if you already do so much on guitar. I think in your last question, you mean should you play an octave above the written melody, and no, you don't need to do that. You can, to bring it out more-- try it and see which you like for which songs, but for a sort of basic rendition, you'll probably sound best in the middle-C-on-up octave, then move around if you want to do your own arrangements with more stuff happening. Also, a good thing to try early on is to play the melody AND part of the chord all in the RH (the top note being the melody), saving the LH mainly for a bass line and rhythmic momentum, not really the whole chords. Especially in ballads, try not to do LH running arpeggios for the whole song. It's tempting, but you have to resist! The difference this makes is huge, it sounds so much more professional. It is, however, more difficult at the beginning! The first few songs this way are pretty hard, then you get a feel for how to find those shapes more quickly. Good luck, have fun.
Topic: Help,from guitar to piano