128GB SSDs have, or perhaps had, the best price/capacity ratio , the 256GB are now at the same level but it s useless to spend more money than necessary, for the difference one could get a 500GB 2.5" HDD, surely that you are some kind of enthusiast that has lot of valuable unused items but most of us will build from scratch and this will rise the cost to the point that the CPU price will often become marginal.
Also, and this is not often mentioned, MLC memory is to be prefered to TLC since it seems that it has better durability.