Id recommend an E46, either a prefacelift 318i, or otherwise get a 325i/328i E46. all other E46 are not worth your while, especially as your first one. interiors are generally good quality, headliners usually the only thing that fails. if anything else inside is wrong then thats a pretty good indication of the life the car as had, as they otherwise dont break on thier own. people arent rough on the interiors but service the car impeccably. if the exterior is a bit scruffy then not a big problem if its a common colour, panels are cheap and plentiful, as are all E46 parts and they will be for another 5 years or so too.
E36 are mostly getting a bit long in the tooth now, though there are certainly some gems amoungst the rubbish. the first 3 series that was designed to protect its occupants in a crash. coupe specific parts are becoming hard to find, but their motors are plentiful, as are sedan parts, tho prices are starting to climb a bit. non specialist wreckers dont bother to buy them any more.
E30s are past being a first car now. highly collectible and reserved for enthusiests these days, even the scuffiest 318i auto sedan is a 3-4k car, and no matter what you buy, you will be working on it from time to time. if you are ready for E30 ownership, you'll know, because nothing else will do.
But above all else, regardless what you buy, please recognise that things can and will go wrong. they are 15 - 20 years old now, and were only ever designed to last 10.
if your budget is 7k, rather than spending the lot at having nothing left in the kitty, you are FAR better off buying a car for say 4.5k and then spending 2k replacing the cooling system, giving it a full service, and then tidying up the inevitable short comings in the interior. Its true that you wont get your money back in the end, but you werent going to get it if you spent the whole budget anyways, so you might as well have a base line established. be carefull of mutton dressed as lamb too. its very easy to make a car look very good, the buyer gets thier heart set on it, but underneath its a basket case.