if you are worried about filling times, i would recommend getting a 4040 ro, it may an over kill for the amount of water that you need, but with a booster pump it fills my 650L tank in 1h 45min, so you could fill your 350 in 600GPD ro off which may be £150? then add the price of a 4040 ro which with the pre filter would cost you would be looking at £1800, whoich would still be a good price for having a system fitted.
not £1800 for the 4040, 1800 in total if GB got anchor cleaning to fit a 4040 instead of the 650gdp, the 4040 and pre filter is about 500-600
You could try and get THIS and have a static setup.