Most states have a limit of about 65' total length, but some are 75'. Have not heard of anyone being stopped for length unless double-towing.
As to license, it is basically on weight, and the big number is 26001 or over, you need some form of CDL, but not the pro truck driver CDL.
Take my setup--F450, GVWR 14500; '05 Mobile Suites, GVWR 16000. Total gross rating is 30500, definitely high enough to require some sort of special license. Do I have one? No.
The weight requirement is based on what the vehicle(s) are RATED for, not what they weigh--
Since I am getting a newer Suites soon that rates at 19000, I have decided it is time for me to get a non-commercial CDL soon----the guilt factor is driving me to drink...
2016 Tiffin 40 QBH
2015 38RSSA, traded
2005 TK3 #1869, 10 yrs of memories,
2017 F450 KR--one more Ford is it
2009 F450 4x4-died; 2010 F450-retired