How to manage storage on a Mac with limited SSD space?

You can move and access your Doc's, Photo's, Movie's and Music to an external drive.

Move your Photos library to save space on your Mac - Apple Support

Change where your music files are stored on Mac - Apple Support

Move your iMovie for Mac library - Apple Support

While moving, storing and accessing files or libraries to an external hard drive is fairly straight forward.

You should use two external drives, one drive for your files or libraries and a second drive to back up the first.

I would suggest getting at least 512 GB of internal SSD storage.

I am using a Mac that has a 512 GB SSD. (That was the only option available in the Certified Refurbished store at the time.). The SSD is a bit over half full. I do have a 42 GB Photos Library on the internal SSD – but no music, TV shows, or Digital Copies of movies (all of those are already on an external SSD).

Since this is a desktop Mac, and it wouldn't be hard to add another permanently-attached external drive, I am not too worried about running out of space. However, if the internal SSD held only 256 GB in the first place, I think I'd be looking at doing a lot more disk juggling.

You purchase the Mac with the amount of storage needed. You can move larger libraries (Movies, music and photos) to external devices to save but it is NOT wise at all to try and save money and short cut, buy what you need. If you don't have the cash, save more or use one of Apple 12 month no interest financing options!

External storage is cheap these days. I don't know what kind of data you have sucking up that much storage, but I would think offloading at least some of it to an external drive would be a viable option.

I think you should learn to manage your computer files and keep them organized so that they won't take up extra space: make sure there aren't too many unnecessary large files, temporary files, duplicate files, etc.

For example, you can use Finder to sort files by file size and delete those useless ones.

To delete temporary files, you can navigate to "Library/Cache". Then select and delete the files.

During the use of the computer, duplicate files will accumulate. Cisdem Duplicate Finder is a reliable and easy-to-use duplicate file finder for Mac. It can identify duplicate photos, documents, music files, videos, archives, etc. and help you remove them with 1-click.

Personally I would not purchase a Mac with less than 1 TB of SSD. I like to keep a minimum of 100 GB of free space to facilitate optimum system and application performance.

KiltedTim mentioned that external drives, both rotational and SSD are inexpensive these days. For budgetary reasons I have a number of the following in 1TB size for external storage and to operate from with a new Mac Mini M4:

If you're considering getting a new iMac consider instead a Mac Mini M4 with a 327"-32" monitor w/speakers. It will be about $650 less than a similarly configured 24" iMac.

Just some food for thought.