Join AOPA and get access to their medical advice program. If you can pass the medical, get your private first, before committing to anything else. Go check out the schools you are interested in. Don't commit to any commercial training until after getting your pvt, since that will give you some baseline from which to evaluate things like aircraft quality, maintenance, plane and instructor availability.

ATPs is more expensive because they use twins for most of the training and they do give you a lot of ME x-country time; however their method of training can be problematic as it relies on a lot of self teaching and there have been people who've gone there who come out with big gaps in knowledge. I did some training with them and they tried to bully me into taking off in very low level vis, their HQ staff was arrogant and pushy, but ultimately I stood my ground and waited till conditions improved and everything was OK.