I would suggest a min 2.5 hp with 50 litre tank.
IME a 2 hp will JUST keep up with a full size HVLP gravity feed but it's working its nuts off & not ideal. You don't want to keep stopping & starting to let the tank refill. Won't run rattle guns etc. OK for dust blowgun & tyre inflation.
Friend in the same line of business has a 3hp which will also run an air sander but you're at the top end of what a 13amp socket will take & whilst some are advertised as plug & play you're better hard wiring into a cooker type circuit to avoid tripping circuit breakers.
Pot below the gun is suction feed. Need lots of air at high pressure & usually generate vast clouds of overspray as a result. Waste of paint if nothing else. A 'Don't buy'.
Go for a full size HVLP gravity fed gun with 1.3 or 1.4 setup.
You get what you pay for & cheapies are generally best avoided.
Good names are Iwata, Sata & Devilbiss - be careful of knock-offs!
My own are Iwata & Sata but £200+ so probably more than you want to pay.
2nd hand is risky, you don't know if they're OK. Spares may not be available & if they are can be expensive. Recently replaced needle & fluid tip on one of the Iwatas & was the best part of £100.
I've heard the Devilbiss FLG recommended but I've not used one. Around £100.
You will need a moisture separator. Surprising how much water results from compressing air & you don't want that suddenly appearing on your nice paint job!
You need to drain the tank from time to time.
Full bore air hose. Plastic can be a PITA in cold weather, rubber is better. A wire framed wind up garden hose carrier is good for keeping it tidy when you've finished. Scrounged both of mine from the local tip.
I have one of these types on each gun.
https://www.ebay.co.uk/itm/1-4-Air-...-Gauge-Nozzle-For-Spray-Gun-Mini/123976294551 Allows for accurate setting of pressure at the gun. Setting at the compressor end doesn't take into account the drop in the hose.