Step 1: To be improved...
The axles: the handcart wheels wobble a lot
The distance between front and rear (too short)...
Not very usable: constant tuning, breakdowns, lots of wear and tear...
Step 2: Improving the hitch
The receiver wheel is quite small: if it will show signs of too much wear and tear, a larger size needs to be selected as replacement...
Step 3: Improving the axles
The wheels have play horizontally.
The wheels can wobble away from a perpendicular position towards the axle.
1: Shorten the bushing (wheel size).
2: Apply lots of grease.
3 (Perhaps later: turn new, cylindrical bushings).
Update: replaced front wheels with better, non wobbling ones: the newer handcarts of the same model use better bearings. Someone needed more space in his shed, and sold his handcart for E 4.- !:)
Step 4: Improving the standard size
As long as traffic is not hindered and protruding loads are marked with a bright flag, everything seems to be legal.
Wide loads (> 1m) are not really legal. But if towed on a quiet Sunday morning, it would not create many problems. Most cops really like the looks of the trailer and don't know obscure laws about them.
There is no limit on length.