should i evolve and stardust any of these gengar´s and gastly´s?

Not the Gastlys. They would cost more dust and candies than powering up a Gengar from a raid and there would not be a big enough difference to justify the extra investment.

If any of the Gengars have Shadow Claw they are worth powering. Shadow Claw is just so much better than Gengar's other quick moves.

Personally I wouldn't power up any of the Gengars either, the last 2 would cost more than investing in one from a raid that would be just as good if not slightly better.

The first Gengar would be missing 8-9 HP depending on it's level, which is "only" an extra Psycho Cut against an Alakazam or Mewtwo.

But considering it's not that much higher compared to a Gengar from a raid (level 22.5), which costs 14k dust and 13 candies to get to from level 20, and you're going to spend at 60-75k dust to take it to 30, why not wait for one that is slightly better? Because then it would also be worth powering up into the higher levels.

At the very least, wait until Halloween ends in case you get a *really* good one.

I have a Gengar with Shadow Claw/Shadow Ball powered up a little above 30. I've used it a few times when autoselect oddly suggests it, but most of the time it just collects dust. I did see an all ghost themed gym this last week that I could have used it against, but out of my way and a pretty rare event.

Power up Machamp, and that 1602 Gengar, evolve nothing.

Just the Machamp. There's no way you can't not get a better Ghastly to evolve and power up. Gengar raid after Halloween event.