While we can point you towards map mods (e.g. Stardew Valley Reimagined/2, Expanded Access, etc), we can't take a piece of one mod and distribute it as another. We can walk you through making your own map edits that don't use SVE's assets, though.
If it's for personal use, you can of course use whatever you'd like! I still wouldn't recommend using SVE as a base even then, though. It has a lot of content all wrapped up together that you wouldn't be using, and isn't designed to be modular. It would be easier to just start with a fresh edit of the Forest map and use it as inspiration. When you give yourself enough room to think things like "I want a garden, but also..." you'll end up with something distinct and personalized even though you started out wanting some exact thing from someone else's mod :)
(And if you do end up wanting to use SVE's assets for something releasable, you can always ask. I find most people are more likely to give permission for things that won't be directly incompatible with their own mods, but you might get lucky.)