It is amazing how quickly trailers start to get heavy. My CDN M101 is rated at 700# stock. I have added a lid (60#), an RTT (150#), a battery box with a group 24 and some other stuff (60#+), an extended tongue, supports, struts, jacks, and bigger wheels and tires. Probably another 100# there. Once you add in gear, water, propane, fuel cans, food etc...you can get way close to 2000# without even trying in a 4x6 trailer.
Do the 3500# if you are going steel frame and box... do it once, do it right, and put an axle that either comes with brakes or can be retrofitted for electric brakes. I am going to swap out the backing plates on mine this year for ones with brakes.
Happy building!!