Help setting up trim marks on various designs on a SRA3 page

Hey all.

(Using Illustrator CS6)

I'm a bit of a newbie to printing designs and recently I've joined up with a print shop to print my paper goods (generally invitations, tags etc). Usually there are various parts to each invitation set and the print-shop guy has asked if I could send them to him already set up for printing on SRA3 size paper. It would be much easier/quicker for us both that way as I wouldn't have to pass through the exact sizes as they vary a lot and he would be able to print them faster for me as it would just be a mater of selecting paper and running them off.

SO, I've been trying to figure out adding crop marks to each design (using the page set-up trim marks way, not the live-effect one) but when I place them on the SRA3 size paper they either don't fit on because the crop marks are so long and it means there's a lot of space between the designs too. If I try to overlap them or even align up the designs to the bleed edge the trim marks go into the next design across. Like, an SRA3 page is designed to take 4 A5 pages, right? Well, after adding bleeds of 3mm and the crop marks, I'm already off the page if I want to print those four designs.

I'm pretty sure the print guy sets this all up on his printer program but is there an easier program for me to use at home? Free please. Does InDesign work the same as Illustrator or better?

I feel like perhaps these are stupid questions but if anyone can point m in the right direction I would be very grateful!

Bex