We should be able to get you going. The good news in the last few days, the release version of Linuxcnc as been bumped up to V 2.8 so now Plasmac is part of the core distribution.
I think your best beat would be to start again. Visit the downloads page and Install the new ISO for Linuxcnc V 2.8 on Debian 10 Buster.
linuxcnc.org/downloads/
That will get you on a common supported platform so people will know what your environment is.
Then I would play around with the Simulations (sims) to get abit of an idea how Linuxcnc works.
You also need to check your latency at this time
The next step is to build a working config so that you can jog your axes and run simple gcode. Because you have a mesa card, the correct tool to use is pncconf which will be accessible from a menu somewhere (sorry I've not tried it out yet). YOu need to know about your micro stepping, and the mechanical details of each axis. Pncconf should let you test your motors and then it will save your config.
Once you get that far, its time to read the Plasma Primer and the Plasmac docs which are both available from the 2.8 docs.
Then run the PLasmac configurator. Sorry but it s so long since I've done this I might be a bit vague on the details but be sure to report back here and someone will help you out.
linuxcnc.org/docs/2.8/html/
