1. One block per 10 minutes means 6 blocks per hour, 24*6 blocks per day (on average). So 5000*6*24 = 720000 .
2. but to use directly lightning, you need to open a channel to your node, so you need to do one onchain transaction for every real, direct user of lightning. Otherwise you are not using lightning, you are using someone's service (for example walletofsatoshi's) and this someone maybe uses lightning. Custodial and easy to confiscate if the state feels threatened enough. Fedimint could be an interesting middle ground between custody and self-custody.
3. I rarely get replies, got kind of bored with nostr and did not check my account.