for fighting the cyberdemon with ranged weapons:
keep dodging until he shoots. shoot him until he reloads, a bit more if you're fast. repeat. Hellrunner or especially Dodgemaster trait, or running tactics will greatly help with avoiding his shots, but make sure you're moving properly in any case! If you need to reload slowly, try to duck behind a pillar.
with a BFG you can probably just brute-force him.
with exceptional accuracy (sniper or AoMC) you can shoot him from out of his range.
phase devices are good to get away so you can use medpacks in peace (techinicians won't need that, but it also works for reloads)
Disclaimer: I haven't fought him in 0.9.9.4, so it's entirely possible that AI alterations make some of this not work.
and congratulations on the first win! I'm surprised it was Haste, I found the base game and several other challenger easier than Haste :)