Not a feature list. These are the parts worth writing down: a protocol other wallets can implement, and the arithmetic behind a decision the wallet cannot make for you.
What a multisig wallet actually is — n extended public keys and a threshold, and nothing else — where those keys may come from, and how to set one up so every device agrees on the address. Also guarded wallets, where one key spends alone up to a limit the chain enforces, which fear each arrangement answers, and what you have to write down because a seed phrase alone will not bring either of them back.
An m-of-n wallet needs signatures from several devices, so the transaction has to travel. This is the open protocol for delivering it — the channel derivation, the envelope, the three messages, the transport contract and a test vector, so any wallet can implement it and interoperate. Two files, no pairing step, no server.
A balance is not a number, it is a pile of coins, and each one costs about 149 sat to spend whatever it holds. What that means, where the 600-coin ceiling comes from, and how to tell when combining them is worth it — including the case where the honest answer is to leave the dust alone.