having the aio pump at the lowest point is always best. if you cannot or don't want to its not that big of a deal especially since that aio can be topped off reducing the amount of air in the even farther.
If tubes need to be at the top. the pump is near where the air will collect. with that in mind i would top off the aio before installing if i can hear coolant splashing around.
How to do this?
i would hold or hang the aio with the fill port at the highest point. run the pump and shake the aio(help move the air to the top). if you can hang it a run the jump for a night its easier. if you have to hold it it may take an 1 hr or 2 of shaking with the pump running to move all the air to the top where the fill port is. once the air at the fill port then open and fill.
Less air equals less noise, better performance, and longer longevity.
Is doing this necessary no. no it is not. i just nerd out on doing those things.
as for your fan placement.
i wouldn't bother with placing the 140mm fans in the front. just the rad with the 120mm fans behind(pull config) makes for easier cleaning. push config is fine too( i think it looks better). performance is the same. so its up to you. Then i'd place the 140mm fans in the top and rear as exhaust