Question 1, thats not a good idea as the offset is probably slightly different.
Question 2, It could cause agro at MOT time as the design strength of the wheels have been compromised by removing metal thus potentially weakening the stud area.
You could argue that its standard for a trailer so it must be OK but I guarantee your insurance company would throw a claim out of the window.
20 odd years ago I clipped a kerb stone with a rear wheel whilst running with 10x6 weller wheels, it tore the rear wheel clean off the hub leaving a small inner section with two bolt holes and a couple of spokes. It was a around 70 mph and by the time the car had came to rest there was only one good wheel left on the car as the N/S front wheel had shed its rim leaving the bent and twisted spokes on the hub and the O/S front had lost its tyre and buckled badly.
I did not hit any thing else on the road other than clipping the kerb with the rear wheel and there was no damage to the car other than resetting the suspension geometry and replacing the wheel arch extensions.
The wheels were not rusty and the nuts were correctly fitted so I can only put it down to sticky 165 tyres on poor quality rims as I could buy them at a trade price of £13 each.
I obviously never used Weller 8 spokes again so my personal opinion would be to shop around for something different.