Check the Status→CBI menu, you have a certain amount of Perf you can use to enable upgrades. The maximum is increased with the CBI upgrades.
Yes, there's no ending.
Certainly not, even the last development update on the forum thread was just a few months ago. The forum thread also details the issue you're having:
Try the git version, it might work better. There are some issues with that version as well, but they'll be fixed eventually.
This is not a bug, it's just a stylistic choice. The missing texture in ZDoom actually looks like this, for reference:
Fixed.
Hold the button. This prompt is changed in the next version.
This is a known issue with Doom 1 and will be fixed in the next beta.
Open the CBI menu and click "Inventory."
Update GZDoom.
If you shoot the light source until it is destroyed, it will no longer be usable. You can do that to fix the issue.
You probably need to update GZDoom. It will only work in 4.3.3.
You need to use GZDoom for now. LZDoom should be able to run it whenever it gets the new font system.
Issue has been fixed as of 1.6.2.
