bitcoin

How many ⚡ channels could we open in a single block?

bitcoinbumbleB

>How much does one channel open take then?

3 block confirmations. Some other solutions offer even 0conf (Phoenix, Blixt).

>How heavy is that type of TX with minimum numbers of inputs?

Here you can calculate yourself: https://coinb.in/#fees

>I know that there are solutions with custody trade-offs too.

I think you don't know about many self-custody LN nodes, here are explained:
- https://darthcoin.substack.com/p/lightning-wallets-comparison
- https://darthcoin.substack.com/p/private-lightning-nodes
- https://darthcoin.substack.com/p/getting-started-ln