Macbook photo storage for digital art, strategies? My wife is a digital artist and has a Macbook pro, iPhone, and iPad, and I am constantly having to clear disk space from the Macbook due to all of the selfies, snaps, cat pictures, and legitimate photos that she takes constantly.  I know I am not alone; these days, cameras are ubiquitous and the Apple product family has some of the best camera hardware and software, and the platform is widely used for digital art.

Her Macbook has 256GB of storage, which is always nearly full; I run a cleaner on it periodically, and have her delete silly pictures she doesn't need, but we shouldn't have to deal with this - non-mac laptops can ship with far more space, and even the current (2017) most expensive Macbook only has 512GB of storage.  If I could tape a 1T usb stick inside the case, I would.

I am looking for strategies to deal with this, other than enabling photo compression/resizing on the macbook (she needs to edit her legit photos).

Her usage pattern is a single Photos library that is replicated with her iCloud account, which is fed with images from all of her devices.

iCloud clearly isn't cutting it, as it's an "all or nothing" proposition - I can't segment the library and only replicate certain types of pictures/directories to her other devices.  

I am open to anything, and willing to pay for a solution if one exists.  I have a large NAS in the home, but she frequently works on-the-go.
Actually, current 15" model MBPs are configurable with up to a 2TB SSD, and the 13" models up to a 1TB SSD.

As for your current setup, if your wife is often on the go then any online solution (be it iCloud or something else) may not really cut it. So, if it was me, I would just use an external USB drive. 

This is portable enough to take on the road, and to keep connected when at home. Of course, you'd want to make sure that you configure your backup regime to include its data in your backups, but this is really the easiest way to increase capacity.

Another option is to rearrange your data generally so that you use your internal SSD mainly for your digital art, and use an external drive for any other large amounts of data (e.g. iTunes music library). Of course this is just a matter of prioritising what's more important to you.

Finally, you may want to check what's using up space on the SSD. You may find that something unexpected is taking up a lot of space (e.g. com.apple.bird, etc). While you can try to determine this manually, an easier way to check this is to use software such as DaisyDisk.

IMPORTANT: I assume since you have a NAS setup at home you've already got a backup regime in place. If not, organise one now!