For free? Sure! 
On the whole, it looks neat and well-cared-for.
The hive mind will have answers!
First up: Do not fire the laser without cooling water flow, not even for a little bit just to see what it’s like. The mirrors at the ends of the tube require active cooling to prevent damage.
If I’m interpreting this correctly, the tube dates back to 2015:
Or it might date to 2020, which is better, but still long in the tooth.
IMO, it’s reasonable to expect the poor thing may not be lasing in the proper TEM00 mode and probably isn’t long for this world. You should certainly use the tube as-is while you get the rest of the machine working, but expect to replace it in the near future.
A casual search suggests the Trocen controller will work, although with some caveats. Reading through those discussions will likely fast-forward you through some setup questions.
Not a chance, because the machine frame determines the length of the linear bearings. When you need a bigger machine, you should buy a bigger machine.
I have LightObject Q600 active chiller that’s barely adequate for a 60 W machine.
If you’re using it in an air-conditioned room, then a slightly less expensive radiator cooler might suffice, but … it will be unable to keep the tube at a constant temperature.
On the very low end, I got along with a cheap icemaker and a big bucket of distilled water for quite a while:
Other folks will surely contribute other suggestions …