Pants for a dark charcoal blazer.
Good reason not to get a gray blazer, especially dark gray. Not nearly as flexible as a blue blazer. With a lighter gray you could wear it with navy or black slacks, at least. But if it's too dark a gray, then you start running into the issue with navy and black of it looking like a mismatched suit. If it's that dark, though, then you could probably wear it with light gray slacks, especially if the material/texture also has some contrast to the blazer material. The right shade of khaki or brown (trickier) could work, too...and if you're a jeans with sportcoat kinda guy, then nice blue jeans could work.
Hope your vest works out, ydarg. If you're going to try to do a vest with a suit using a vest other than one made with the suit material as part of a three-piece, you can google image "odd vest suit" for some ideas. Easier to do an odd vest (term for a vest not made as part of a suit) with a less formal suit or sportcoat, though. Gotta avoid looking like you're headed to prom or a Men's Wearhouse wedding.
Also, whoever said to check out the big and tall tie section and tiebar.com was right on. Tie Bar has big and tall ties, BTW. And the ties are thick enough that the four-in-hand referenced by spracne won't look too asymmetrical, if you're not into that.
