rewiring

[jetblue319]

Hello
i will start to rewire my 86 v20 c/c o/b soon. i would like some opinion on wiring. i looking at 12 gage marine wire in color code, as per ABYC throughout the whole boat. i will relocate two batteries (starting and deep cycle) to behind the instrument panel, in c/c. with a Blue Seas "add a battery kit". using Blue Sea ATO fuse panel w/ neg. bus 12 slots. (thinking ahead for added features). A planetronic toggle switch panel 8 position. ,
Questions 1: what gage battery cable should i use since im running cable about 15-20 feet (thinking of using 2 gage battery cable).
Question 2: what main supply fuse should i use to be in compliance with the ABYC 7-40-72 rule. Im not planning on running any big motors.
Will be removing/cutting out, the rest of my fuel tank today.
BTW West Marine is having a 3 day sale on primary wire.
thanks
jet