subs: 3 12" hx2

do i need 4" or 6" ports?

tuning suggestions also welcome...i was thinking 6 ft^3 @ 34 hz

For a general rule of thumb with aero ports I try to have 1/3 or more port area as cone area. so 3 4" aero ports, or 2 6" aero ports would be my minimum recommendation.

should i try using 3 6" ports? or would this be too much.

I would recommend using (3) 6" ports for a 6cu ft box and two 12s.

Some people determine port area based on driver surface area, some on box size. Most everyone will agree the more port area you have the better. I've read a few articles discussing measured distortion even using as much as 1/2 the speaker cone area in port area.