One of the problems I’ve encountered in the past when using RAMPS electronics to control a dual-extruder printer is the lack of sufficient fan support. Dual extruder setups can require a few fans, usually one controlled fan (for cooling the print) and one or two always-on fans for cooling the hotends. Adding a second hotend takes up the 12V MOSFET usually used for running a controlled fan, leaving no option but to solder directly to the 12V lines on the board – which removes any control over these fans.
If your printer has an always-on power supply (like a regular LED-style power supply as found on most printers) then these fans are going to be running 24-7 unless you manually switch off the power. I had to deal with this for a few days while testing the MK2 printer, and I decided to play around with the problem and see what solutions there are.