Framing in a home's crawlspace

Looking to take some time in the new year to frame out an area of my "crawlspace." It has about 7.5′ clearance in height, so it’ll be tight… but my goal is to make a workbench area for myself and would like the area to feel cleaner / less dusty and crawlspacey.

Here’s hoping this drawing helps… the dotted lines are where I’d frame… the doorway leads to this unpermitted bathroom the previous owners built (whose sewer ejector pump broke and was installed under the tub, so that’s for another post).

I mainly have two questions here as this crawlspace is shared with the water heater, the heater, and the foundation for our chimney:

• Opening the door to the crawlspace the heaters and chimney are to the left. I’d like to frame around them but still leaving access (like folding closet doors or something) to get to the space. Do you think this poses any significant fire hazards? I won’t be framing right up to the utilities of course.

• Also, somewhat related, is it bad to frame around the foundation to the chimney too? It has an ash shoot that I’ll keep access too, but just wanted to make sure there

Anyway, thanks for your time. Happy to respond with any follow-up questions. I imagine after framing the area will be long and narrow… maybe like a standard hallway, but wider. Hope that helps with imagining it.