I play a little carnatic in my guitar. I'll be happy to share the
things I came across with u.
First, It'll be better if you are certain about your knowledge and
practice in carnatic 'on' Veena. If you have clear ideas about
ghamakams etc and if u can play them comfortably in a veena, that
knowledge will be certainly helpful when takingup guitar. Because
getting help for those matters in a guitar is a bit difficult
Second, have you already bought a guitar?. Choosing a guitar is very
important. Electric/Acoustic.. Acoustic wont sustain much, that makes
it difficult when playing ghamakams and long stretched carnatic
phrases. But the 'tone' of an acoustic guitar will be beautiful,
natural and quite comparable to a veena. An Electric guitar sustains
its notes longer, so one can play carnatic with out doing much damage
to it :). But it depends on individuals' taste. One likes electric
guitar and the other doesnt.
So, I'd suggest you to 'know' about guitars better. Different types of
guitars, like acoustic (u need to get a cut-away guitar in this case),
electric, also spanish/classical guitars.
Apart from surfing internet, you may also join in some local guitar
class. That'll give u a better idea about the varieties and which one
suits your taste and which one doesn't.
Tuning, Fingering, ways to play gamakhams etc all are subjects for
discussion. Let's discuss them one by one.