Theres no specific amount of tension that is always enough. Its very dependent on the board, ride conditions, rider weight, gearing, wheels, belt width, etc.
As for idlers and lips
Generally, your wheel pulley has the lip on the outside. So if your motor pulley is a single lip unit, put the lip on the inside of the board.
For adhereing idler pulleys, i personally juat use the bearing face rather than gluing a tube or whatnot over, but if you must, green loctite and a friction fit will hold nicely.
I don’t think you need to be picky to have the idler cover the full width of the belt. Two 608 bearings will be fine.
A minimalistic drop of super glue
This maybe won’t help your case but I dump it here anyways. Did this to my daily driver with 255 12mm belts. Always suffered brakes due to belt skip. But not anymore.
I got the idea from someone else here I think. Can’t take any cred.
Bearing size and pulley must match. this is the perfect combination so there is a small airgap in between.
Temporary running without my belt covers now. It’s sucks. I pick small pebbles every 10km. It’s noticeable when a stone gets squeezed between pulley and this bearing
But if you were able to get that bearing in the perfect spot, heck ya dude, nice job!
