Question 4 ram in dual channel

RAM is only guaranteed to work in the kits its sold in, so buying 2x8 now with plans to add more may not work, most of the time it does, but something to consider.
Ideally, you buy however much RAM you need now, not only do you not have to worry about it not working, but using only 2 sticks ever so slightly reduces demand on the memory controller compared to 4 sticks.