100 litre tank would be about the minimum, but thats not the issue here. You need to check the air consumption of the tools you'll be using i.e cfm (cubic feet per minute in old money or litres per minute new money) then add on a bit and buy a compressor at least that output FAD (free air displacement). This should ensure your not using it faster than the compressor can supply it.
I bought a 14cfm with a 3 hp motor and 150litre tank (from Northern Tool at a good price) it just manages to maintain 50psi with the air chisell / needle gun. Chisel supposedly rated at 9cfm. Other tools like ratchets, drills sanders etc done usually use as much. Get a drip oiler and set for about 6 drips per hour. Oil tools before use as recommended. Always drain the compressor tank regularly to avoid rust. I put a few squirts of green oil in the tank every 6 months or so, to emulsify any moisture. If you going to be spray painting you'll need a dryer / water trap just before the spray gun.
Hope this helps.