Sure you can tee in a lot of line to other equipment. Only you have to be sure that the 'draw pressure' of the booster pump doesnt suck air back through the 'other' devices and cause a slug of air to hit the high pressure pump ... or worse the RO membrane. Such will work if you have valves on the discharge of the 'other' equipment that is 'tee'd into' the RO unit.
Using a 120v pump has definite downsides, as when you have 120v available you usually dont have 'decent' and low particle water to draw from (harbor marina, etc. etc.). Best is 12vdc or engine driven so that you can reliably take on water that has some degree of low particle burden - out in the open ocean or in some remote & not-close-to-*pooping-in-the-water-people*, location . ;-(
A high pressure deck wash pump is ideal to feed the lowside of a high pressure RO pump; and, you have the availability of the deck wash when the watermaker is not on.