As regards the overhanging mast to rear…
Up to 1m is fine
1m to 2m needs a white flag on the end
2m to 3.05m needs a marker board (illuminated at night)
Not usually an issue when towing with a car, where a properly arranged trailer will put the mast over the roof at the front instead, but it you have a van or a camper or whatever then you might need to rig the mast further back, as above.
Agree with advice re bearings and spare wheels, one further note to add is not to launch the road trailer immediately after towing any distance, especially in salt water. If the bearings are warm then quenching them in cold water will cause them to cool and suck water in, which the seals won’t resist (as they are designed to keep grease in, not water out). Let them cool first. Ideally, have hubs with a grease nipple and put a SMALL squirt in with a grease gun from time to time to keep the bearings fresh, but don’t put loads in as this causes more bearing failures than anything else!
(Another good plan is to keep the spare wheel bolted onto the chassis of the trailer on a suitable frame).