I would use 4 floats and go much wider. At least 8', but a you could get by with a 10x10, 8x10, 8x12. With four 3'x4'x18" floats you should have about 3800# total capacity, and 1900# useful capacity and be much more stable being wider.

Since it is a float, you can always "add" more sections or gangways.

1.8 acre pond with CNBG, RES, HSB, and LMB
Trophy Hunter feeder.