Not as familiar with the 3.5e rules and I don't have my rule books handy, can someone remind me of the buying rules for feats?

You acquire feats at level 1, and then also every 3 HD. So level 1, 3, 6, 9, 12, etc. Also you might get bonus feats depending on your base class.

Are your initial feats (Lvl 1) based upon ability modifiers, as with intelligence and skills, or something else?

Not usually, no. Though some might have pre-reqs. Like Power Attack requiring STR 13 or higher.

And humans get a bonus feat at Level 1.

Thanks for answering my questions everybody.

In the future though, perhaps use the Quick Question & Answer thread at the top of this forum. It exists for just such a purpose as this.

There is a variant rule for flaws, which can be taken at 1st level and grant a feat for each flaw taken. But that's a variant rule, from Unearthed Arcana, and is probably not the norm for anybody.

Actually, there are quite a few people who consider flaws the norm. Dunno if they're in the majority, though.

Most games I apply to don't allow flaws. But my personal experience doesn't equate to "the majority," so you can probably take it with a grain of salt