Hmmm – all very interesting this thinking and designing and research – I have picked up a few little gems especially about the Ramps 1.4 controller board – Lots of different manufacturers each one builds the board slightly differently.
So research has found – not all suppliers put on a two pin header next to diode d1, this header gives you a 12v supply which you can use for powering say a cooling fan for the ramps , or maybe some leds.
Also the A4988 pololu drivers in which most people put a heatsink on top of are apparently designed for being heatsinked underneath which looks pretty near impossible.
Not all A4988 boards are the same , some will work with ramps 1.4 and some just wont , and also there are fake ones out there too.
Plus if you want to do long prints that say take 24hrs or so then you need to change the 3 voltage regulators.
If I have missed anything I will put an update on.