the size of the compressors tank doesn't dictate the volume it can fill. I don't know the math off the top of my head but I suspect a 5L tank of air compressed at 120psi will fill a 10L tank at 50psi in one shot with out needing the compressor to turn back on. But regardless, you just run the compressor until the pressure pot (regardless of size) reaches the pressure you want.
The only time the tank on the compressor becomes a factor is running air tools. What happens with a small tank is you're grinding along with an angle grinder using 30CFM at 90psi and after 15 seconds of use you have to stop what you're doing and wait for the compressor to fill the tank back up so you can keep working.
Regardless, grab what you want... that compressor's specs are pretty awesome. You will have more than you need for many uses i suspect.