Wouldn't bother with more than 1 as it will be more than enough for a featherweight. The other issue you might have with V belts is the size of the small pulley as they typically don't like to go around very small radii. I'd consider small timing belts as another option.

Bolts, keyways, clamping mechanisms are all potential methods to attach the pulley. The disadvantage with welding is that it's a nightmare to remove the pulley from the weapon if you have to.