It all depends on the yield. in less than 50 bu/ acre, I would say 30ft would be just fine.
50-100 bu. 25 ft would be the better choice, and in 100+, 21 ft is what I would think would work best. we run 16, 18, and 20 ft direct cut auger heads on our small engine L2s doing 100-150 bushel/ acre barley and 100+ bu. wheat here in Idaho. big engine with a draper could handle more width.
Weight shouldnt be an issue. they made 8R30 cornheaders for these, and IIRC they weighed 4500-5000 lbs or so.
for counterweight, you can put the custom harvester special dual fuel tank kit on, and have a shutoff on the back tank, and keep it pretty full. dont be like JD and pile a bunch of useless cast iron on.
