From what I’ve read, M-of-N multisig addresses are possible in bitcoin. But nothing I’ve read talks about the limits of that (eg I’m not sure if there are limits to M and N) nor whether there are more complex forms of multisig.

For example, something I think I would like to do is have an address that can be spent on in the following conditions:

1. Address A signs it, or
2. At least 3 of B,C,D,E,F and G sign it and H also signs it

This would allow me to have an address I can use normally that also can be accessed by a number of trusted 3rd parties in the case that Address A gets lost or destroyed. This would be useful to back up your bitcoins by distributing some keys to a number of friends (B,C,D,E,F,G) with an explanatory note and final key in your will (H).

Is this kind of thing at all possible in Bitcoin?