Just baught a 1966 straight 6 coupe and had a few questions

[1966stangkid]

my dad and i just baught a 1966 straight 6 AUTO coupe. the cars in decent shape but needs some work. as of right now it wont start. however the engine still turns and the lady we baught if from said she had fired it up about 2 years ago. the problem was the trans. was slipping. so, she thought it needed to be relplaced. thats about the time when she parked the car and let it sit for 3 years (said she was tried of puttin money into it)... so if someone could help me first with a few tips on starting it....and tell me what could be wrong with the trans, or if the trans. is done, can i just swap it for a 3 or 4 speed?.......or should i just try and re build the old auto one? thanks for any help you can give im sure there will be more questions later on but thats all i need to know for now.....ill post some pics when i get her pretty.