I'm on Mission 8 and after a close call in the last mission, have to start the level on my last life, 0 shields, and 8 health points. I have been trying for 2 days to beat this level but the instant I do anything shy of perfect.....dead.....start the whole level over again. Is there any way to get more lives or do I have to start entire game over again?

There are a handful of cheats: https://www.gamefaqs.com/pc/3397-star-wars-dark-forces/cheats
You could just use invincibility until you are better off.

Although, if I recall correctly, the game saves the "starting condition" for every level. So, you could just play Mission 7 again to improve your start into Mission 8. I basically started over a few times until I found most secrets and extra lives in the starting levels, so I never ran out of lives.

It's my first time playing the game and I have been playing with DarkXL. I'm probably going to start over running the game in DOSbox because I am just realizing now the amount of things missing from DarkXL. Those original controls are gong to take a lot of getting used to though...

Try this setup https://www.gog.com/forum/star_wars_dark_forces_series/remapping_keys_for_dark_forces/post24

It isn't full mouse look but it is a lot more comfortable than the default controls.

I recommend also using GlovePIE to map secondary fire, weapon switching and looking up and down to the mouse itself. This was the most comfortable setup for me. Looking up and down takes a little bit of getting used to, but I just could never get used to using keys for it.

You can either use TQuin's Dark Forces Plus which comes pre-packed with everything you need already set up. It inclused some mods, but those can easily be deleted it seems.

Alternatively you can just install GlovePIE and run a script for it yourself, for which I used this rather simple guide: https://steamcommunity.com/sharedfiles/filedetails/?id=286364447