Just built something similar for my rig. Used a 65 gal tank and then got a 12V electric pump (44 psi, 4 gpm) from Northern Tool, a battery box, and a 12V battery. Mounted the pump to the battery box and wired in a switch, so the pump box and the tank can be placed where needed and the machine can go do something else.
That will work fine, I just made one out of a 55 gal plastic drum, I have an 8 ft boom i built yrs ago for a 25 gal tank sprayer. The only issues i have are my spray tips get clogged a lot. I just bought a removable screen filter to go inline, Hopefully it will help, The suction end in the tank has a filter , but stuff seems to get past it.
FWIW: I strap mine into my 4n1 bucket, and wired up a Northern Tool pump via a 12v socket under the dash. If I were doing it again, I would use something other than the "normal" 12V lighter socket as vibrations does occasionally work the connection loose. I tend to do my spraying as spot spraying on foot.