For the tone knob, 250k and 500k wont make much of a difference. It WOULD make a difference on the volume pot, however.
Its perfectly alright, it won't hurt a thing. 500k pots just let more treble though than a 250k pot. 250K pots are generally used for single coil guitars, since they have plenty of high end. Humbuckers usually sound rather dark and muddy with 250k pots, so 500k pots are usually used with humbuckers (or a guitar with both humbuckers and single coils)
But your signal path doesnt really travel THOUGH the tone pot, so it wont make much of an impact whether its 500k or 250k on the tone pot.
The trem claw should be grounded to the back of a pot, either the volume or the tone, it doesnt really matter. I'd probably do the volume, just to help keep the grounds centrally located to avoid confusion.
As for the trouble, I tried to find an existing schematic to "mod" but I couldn't find one I liked or that was laid out very clearly, so I just started from scratch. Microsoft Paint dude

Once you understand everything, its easy to whip up schematics like that.
Totally look into that book, it explains just about everything. I found it at the public library (while I was supposed to be doing research for an english paper. . . lol) if its not there you can just get one off the internet.