4K to spend and I don't know what to do with it!!!

[stilscream]

Personally, depending on how much gear you have already:
None:
T2i $450 used each
580 ex ii $350 used
35L 1.4 $1300 used or 24-70 f2.8 $1200 used
Later, I'd upgrade to 5d mk iii for low light ability.

Lens collector:
5d mk iii $3250 refurbs on eBay
50 f1.4 $300

[RLPhoto]

Easy, 4K is plenty.

100mm F/2 - 500$

24mm 1.4L II - 1500$

5DC - 700$ (or the mkII if you can afford it.)

1x 580 EX II - 500$

Total - 3200$ more or less.

Ditch the 18-135MM, Kinda slow for weddings.