OP: add up all storage- the 256GB internal and the total of those usb sticks. Then, multiply that by about 3 or 4. That's the minimum size you should consider.
Then, think about the future. Is the minimum possible enough to cover your needs for how long the HDD you buy might last- which can easily be 8-12 years from now. If that makes you think your backup need will grow- and it probably will- buy for 5-8 years from now instead of right now. Will there be more than just your computer to backup in that timeframe? Will you have a second computer that should also be backed up? If so, best estimate the combined storage and then multiply that by 3 or 4.
Example: lets imagine your 256GB plus "USB Sticks" = (wild guess) about 500GB. Multiply by 3 or 4 means right now you need 1500GB-2TB. Extrapolate need for maybe a half decade from now. Is that 500GB overall maybe 1TB in 2029 or so? If so, then I'd be thinking 3TB to 4TB right now. Having too much storage is a much better "problem" than having too little.
In US dollars, I'm seeing 1TB drives for about $50, give or take maybe $10-$15. A 4TB HDD is about $100, give or take about $15-$20.
Now, I don't know your situation but +$50 seems like it should not be much from about anywhere in the world. Take a couple more weeks before buying and save $15 bucks a week to come up with the difference. Then you can buy ONCE and probably be set for backup storage for the next 8-12 years.
You wisely say you want at least 2 drives. And t
hat's right: the 3-2-1 backup concept mentioned in #14 is THE RIGHT WAY to go with backups. So if it takes a couple of weeks to scrounge up another $50 for one drive, give yourself a couple more weeks after that for drive #2. Then you have
TWO 4TB drives. Backup
everything to BOTH of them and get one of them offsite... to regularly rotate with the first one so you are reasonably up to date at all times and can almost entirely recover from fire/flood/theft scenarios that takes out BOTH computer + backup HDD at home/office.
OK, now let's take cost the other way
If money is that tight, consider other options. For example, returned/refurbed drives can cost a lot less than new one. A 4TB WD that comes up in a search on Amazon for $114 is available for $78 "Used-Like New" on Amazon as I type this. And I bet with some solid shopping around, I could track down 2 new or "used-like new" for maybe $130-150 for the pair. Isn't seller competition grand Apple people? Remember when we could do that with RAM and internal Mac storage?
Lower? Consider a bare drive dock and bare drives, which I use myself. It's easy to find 4TB HDD bare drives NEW for around $75 and in some cases less. "Renewed" can bring that down to about half that. OR, if you are willing to apply that approx. $100 each referenced above, $100 for "renewed" would buy you upwards of 12TB or so per drive. I'm not necessarily arguing
FOR "renewed" HDDs though I have purchased a few of those myself and they've worked well for years.
A
good dock can be purchased for $30-$50. Pick yourself up at least one
HDD plastic case for the offsite storage packaging (that link is to a 5 pack).
Unlike anything you might buy from Apple for much more than up to $200, just about NONE of it will still be working for you in 8 years... or you will have felt compulsion to replace it long before 8 years. Scratch up the extra cash and buy a little overkill storage. 2029You will be glad you covered your future need than only your 2024 need with hardware that will probably still be working for you in 2034.
