"Safety is about having a well maintained vehicle in good condition more than anything else. The performance, or lack thereof, will drive you toward a more capable vehicle LONG before what you are driving is truly "unsafe" if you are anywhere near the ratings."
^^^ This.
That being said, were it me, looking at the 2021 3500 SRW ratings for a 4WD Crew Cab Standard Bed: 12,000 GVW, 29,700 GCVWR, 21,300 max 5th wheel rating, 4,185 max payload: I'd probably shoot for a trailer with a (trailer) GVWR of 16,740, probably a bit less...i.e. so that 25% of the trailer's GVWR = the max payload of the SWR 3500.