I agree that you really don't need more than one or two sets to get started - I tend to have fads on a particular outfit and wear it incessantly until something else takes over! The only time you really need other things is if a certain colour, say, is requested (I get asked for all-white or red sometimes) but this really isn't that common IME, the most common request I find is for stockings and suspenders (and whilst I'm a confirmed FF girl, which isn't cheap, the vast majority don't know and don't care about the difference -
Stockings HQ is brilliant and sells great suspender belts as well).
I can't wear holdups because the sticky stuff gives me a rash and I find that clients don't like them, but obviously not everyone's clients are the same! With summer coming, bare legs are as good as anything unless you've been requested otherwise (and keep a couple of pairs of tights handy - I have guys who like these too).
From an outerwear point of view I wear a plain black pencil skirt and either a silk blouse or a button-up cardigan (with jumper if its freezing), or a nice dress in summer - the black stuff is habit really because I can have a pile of separates that go with each other so I don't have to think about it! And wear heels, even if you take them with you and carry some flat pumps in your bag to wear for travelling.
Agree completely about makeup - I hardly wear any and your client won't thank you for foundation streaks on his clothes.
Good luck and let us know how you get on!