Could anyone tell me how much size I would need for a backup on my M1 MacBook Pro 512GB. Do I need a 512GB USB or does it somehow compress into a smaller size?
The rule of thumb is that you want at least 2x the amount of data that you’re planning to back up.
Also: I assume by “USB” you mean one of those thumb drives? Those are fine for transferring files back and forth between computers, but they are not reliable for backup storage. You should either get a proper SSD or an HDD if you’re on a budget.
Get a HDD with 2TB at least, you don’t backup it only once, right??
If you use Time Machine (which you should, it automates the process, is very easy to use, and trivializes backups for the novice) you’ll want more than 512 GB on your backup drive. Time Machine takes snapshots so if you need to do a restore, you can cycle between your machine at different states.
You can buy a much slower HDD for this. You don’t need high performance on your backup drive. It will save you a boatload of money because HDDs are cheaper than SSDs.