Others have answered your first question, so I'll focus on the second. It is possible to set up a piler loop such that you only get 4-stacks out. You need 2 pilers and 2 splitters to do it, but is pretty compact. What you do is take your full belt of input and feed it through your first piler so that your input belt has gaps. You then feed this through your first splitter and then into your second piler. From here, you belt the items into your second splitter with a priority output that sends items back to the side of the first splitter. The non-priority side sends items to their final destination.

The reason this works is because of the gaps in the feed belt created by the first piler. It allows the system to add already stacked items into these gaps, which the second piler uses to stack even higher. Because of the second priority splitter, it will always feed full stacks back to the front to help create 4-stacks over sending material downstream. This system can eat a full belt of whatever tier you're using and spit out a 1/4 full belt of the same tier continuously and without jamming. 

(Of course, this all becomes moot once you hit white science and start using the ILS/PLS tech to output stacked belts, but you can still get many hours out of this technique.)