3-axles are nice and stable, I've done a fair bit of towing with @Escape's 3-axle Ifor TB. The biggest downside is manoeuvering on uneven surfaces, it'll swap the wheel it's pivoting on on a whim, which can be a bit annoying.
And seconded with the lashing points, it could really do with a bit of holesaw treatment.
Overall: go as big in size and capacity as you can get away with, you'll never regret having a trailer that's slightly too big for the load.