Is it ok if I use the same username (i.e. wallet address) for all my miners in a p2pool? And if my miners are weak independently, do having them use the same username help to avoid the situation of not getting paid because of too low hashrate?
It might be hard to understand, but the chance to hit a block after 1 minute is just as high as hitting it after 1 hour. But if someone has twice your hashrate they also have twice the chance of hitting a block. So technically you will earn the EXACT same doing centralized mining, P2P mining or even solo mining. The only difference is the fee that is applied, centralized usually having the highest, then P2P, then lastly solo mining which is feeless.
It also takes the shortest time to see earnings in a centralized pool, average in a P2Pool because if ANYONE hits a block you get your share of the earnings. And lastly the longest in solo mining because you have to hit the block, but you get the whole value of it.