Hi, uh I would suggest that you not buy a cube MATX case. Why? Because like you said: you don't think the available fans/fan slots are enough to cool the PC adequately and you're probably right.
So I would also suggest that you buy a case that has at least one 120mm fan and another 80mm, if not a 120mm.Also, if you were to do the liquid cooling, the tubes would further restrict the already restricted airflow causing even more problems.
Especially if you're doing any gaming you'll definitely need the added cooling. If you're not gaming, then you should be ok with the standard air cooling.
But, these are only my opinion and you do whatever you like and I hope it works out for you. Good luck!!!
If you want a mini case, you'll need a copper heatsink and if possible, a power supply with large side fan for helping to remove warm air. If you don't need a high end cpu for your normal functions, then a celeron or sempron would be much easier to work with.