Update:
Did some tests. Loooking good.
The Arduino and other board together pull about 500ma - even with the relays operating.
The solenoids each pull about 700ma
The pump pulls 2A - well less, but to keep things workable.
I don't know if I should put a 7805 on the Arduino as while testing, a couple of the chips get hot.
Though the heat has to be disipated somewhere, I would prefere not on the Arduino.
Also will I need de-coupling?
Maybe a low ohm resistor and a cap to the electronics.....?
I shall get small caps for the solenoids and relays, and put a largish electro' cap on the supply, but would that be enough - without getting too complicated?