+1
Combining your 3 house banks into one makes good technical sense. If possible, have the B+ from the sources/loads at one end of the bank and the B- from the sources/loads at the other end of the bank.
Install the shunt for the Link 20 between the bank B- and all of the sources/loads. This will count the coulombs in and out of your house bank. Connect the voltage sense B+ (position 6 on the back of the Link 20, violet wire if you used the Xantrex cable) to the starting battery's B+ and you can sense its voltage which is sufficient for a starting battery. By the way, my version of the Link 20 manual has a typo on the
wiring diagram on page 34. Position 6 is for B+ voltage sense, Positions 7 and 8 are a twisted pair with Position 7 (yellow) on the battery side of the shunt and Position 8 (brown) on the load side of the shunt.
Hope this helps.
Charlie