Options and solutions for a really old brick chimney?

I'm looking for thoughts, ideas and options for a really old brick chimney. I want to use it,  It has basic masonry, all the way up. No liner, no pipe. As I see it right now if I want to use it, installing a multi-hundred dollar liner is the best option. However I do not know if I can install a liner like that right now. It would improve my quality of life this winter by leaps and bounds if I could use it safely, but the inability to clean it out properly really worries me. A long time ago there was a chimney fire in this old brick chimney, and the fire was quickly put out, however I really want to avoid something like that. One thought I had was to run a thin pipe up through it and force the smoke to only be able to go into that, but The chimney gets really tight, with a width of 6 or 5 inches, so it will be hard to get anything up there at all. Another thought I had is doing some sort of chemical reaction that could react with the creosote and melt it off, or burn it up in a non dangerous way.

Some pictures for reference are attached.

Any thoughts or ideas are welcome!

Joshua, what is your plan for the fire end of the chimney? Just using the original fireplace? Or a wood stove or insert perhaps?

The mortar looks a big dodgy. That and the fact that there was already a chimney fire gives me pause. Personally, I don't think I would trust it without careful scrutiny.

Hi Josh;
Any wood burner other than an RMH would be too dangerous to use without an insert.
An RMH should have a chimney temp of 140-250, well below wood ignition temps.
You would certainly want a good video of the inside of that chimney.
Can it be inspected from inside the house?

This video compares the temperatures of the inside air, outside air, rmh and pipe exiting house.  I'll be building one soon!