As Vladis said, the jumpers on your batteries tying them together should be much heavier than the
solar wiring. You can get pigtails specifically for that at most auto
parts stores, even, for a few dollars each. Your
Solar controller wiring should go to the + of the one end of your bank, and Negative at the other, if I remember correctly. That's how mine is (same controller, but I have 2 batteries instead of 4).
When in doubt, fuse. I have it fused at the
battery just as you suggested, I figure that I might not HAVE to, but I'd rather be safer than sorrier.