You can save it where you like as long as you can find it.
4K is quite a large texture and if you don't have much ram your machine might struggle if you get a few of those in it.
I believe the maximum resolution for a single texture is 8K (8192).
BTW I noticed you have the resolution set to 4000, Maya really likes textures to be the power of 64 so it should be 4096 although that seems a little large for your still unless you are planning a HD image.

Looking at your layout I think you could rearrange them to make better use of the space and make them slightly larger,try and create a square with them which will allow you to scale them as large as possible.