You should consider what you want to do with your trailer. If you want to park it and stay put for weeks / months at a time, then you probably want a longer trailer. If you want to travel, I would suggest that you consider a 24' - 27'.
It is not just weight, but length is a significant factor when traveling. The longer the trailer, the harder it is to maneuver. Buying fuel gets more complicated the longer the trailer. A few RV Parks only permit trailers over 25' (trying to keep out "campers") and less than 10 years old. However, we have never been turned away because of the age restriction once they see our restored 1963
Airstream. Other parks (like National Parks) have restrictions limiting length to a maximum of +/- 25'.
Concerning the axles.... Since you want a vintage trailer, it is likely that it will need a new torsion axle unless it has been replaced in the last decade. There are many posts explaining how to determine the condition of axles. Andy at Inland RV is an expert and would be happy to assist.