Some more information please. What drives and video card come with the “minimum” kit? Will help with commenting on those potential upgrades.
For you question on RAM, motherboards tend to have 3-4 slots for RAM. A 3 slot board tends to want all 3 RAM cards the same size. A 4 slot board tends to want RAM cards to be matched pairs, 2 of a size in the 0-1 slots and 2 of same or different size in the 2-3 slots. Then you just add up the RAM.
So you may have to replace smaller RAM cards with larger RAM cards if all 4 slots are full. Increasing your RAM, as far as bang for your buck, can be one of the cheapest improvements to your system to a point.
