Work out what power you need then add more for safety.
The Arduino generally uses around 25mA, a HC-05 can draw 40mA.
The valves can draw anything from about 30mA up. The Chinese valves I like use about 250mA and I normally use 4 at a time.
This means if I have all valves on at the same time they need 1A. The rest of the circuit needs around 75-100mA. Adding a bit of margin I went for a 12V 2A power supply which has worked well for several years now. I also have a 24V 5A power supply but I do not use this that much.