You are one of the smart ones doing your reserch befor buying well lets see a good starter constrictor depends what you call least several feet long there is ball python 4-5 feet give or take verry nice snake. A common boa constrictor BCI 9-10 feet also verry nice snake.if you hear that a burmese is a good starter snake RUN as fast as you can LOL there are nice snakes but but get way big like any where from 12-23 feet. if you want that in the future get a boa to start you will se just how strong a 8 foot snake can be.
As for housing I say a 20-25 gallon could give you a good start but later you might go on a adventure ade build your own cage
and a heat lamp over top I dont belive in heat mats but there are alot of ppl hear have good stories about them.a hide box and some rocks and branches also a water bowl that is big enuf for the snake to soak in
I am shour that there will be other posts with a lot of good advice so yous your judgement and and ask if you dont understand