That's the interesting thing. I've written very LITTLE, so my initial forays into putting ideas together have been to bastardize other songs that I know.
I'd worry less about trying to write on guitar and try to just try to write in your head.
Write a different guitar solo over an existing verse or chorus where there is no solo.
Jam with the hot rod car engine that has a Pantera drum and bass groove going on.
Write a simple melody and keep repeating it while making variations every few repeats. Maybe eventually hear a Phil Collins tom feel drop into some drum pattern under it eventually. Basically jam, with yourself (don't go blind), as you take inspiration of your own making and keep adding to it. Even if you realize you just zoned out for 30 minutes doing it.
Writing in your head is much easier. There are no limits. Heck, there are/were things I jammed in my head that I had no idea how to make happen with instruments (usually a synth that needs you to program it). But don't worry about if you can reproduce it or not. Don't worry about if it sounds like Dr. Feelgood v1.01. Just jam it out in your head.
Whether or not you get it "to tape" really doesn't matter.
I just need a MUCH better option for programming drums. What I have to work with is extremely limited.
There were a lot of stages in writing for me. Saving up for a synth and drum machine was probably a big milestone. I wouldn't worry about securing the best possible setup. Being able to write down drums on paper means even if you don't have a V-drum setup, you can probably get it down somewhere. And a real drummer is almost always going to make your drum parts better with all the nuance they add.