Backing up Bitcoin using only private keys?
It depends on what kind of wallet you have.

Traditionally each private key was generated randomly by your wallet software. In this case every private key needs to be backed up.

Recently deterministic wallets have become popular. Deterministic wallets randomly generate a seed, and then use that seed to deterministically derive the private keys in a cryptographically secure way.

To answer your questions specifically:


It depends on whether you use a deterministic wallet. Traditional method: If you make multiple transactions, new keys are periodically generated and these need to be backed up too. Deterministic wallet: backing up only the seed is sufficient.
Also depends on wallet. Traditional: back up every key. Deterministic: just backup the seed.
Yes. Private key ownership = ownership of the bitcoin held at the addresses derived from those keys. If you don't have the key, you can't spend the bitcoin.


In Bitcoin Core, both kinds of wallet can be sufficiently backed up by backing up your wallet.dat file. There is an HD (Hierarchical Deterministic) symbol in the bottom right that is greyed out and crossed out if you do not have a deterministic wallet.

Since you want to backup on paper, maybe Bitcoin Core is not the best solution for you. You could try using a wallet that implements BIP 39 (there is a list of them on the deterministic wallet article), which derives the seed from a human-readable list of words. In this case, writing down the seed words is a sufficient backup.