It is generally suggested that you have 2 hrs worth for permeate storage, so a 600 would mean 1200 gal. In use I found I rarely use that much. For my 250 I started with a 550 gal tank and never ran out, until I bought a flue pan washer, it uses permeate to clean the flue pan, once thru and flows to drain. If I run that for 90 minutes I go thru about 300-350 gal. Then I got a 1000 gal tank and it serves well.
My RO came with 4 prefilters, one in it and 3 extras. I soon bought a full case of 25. Mine came with enough soap to last a season, and also came with enough acid wash and preservative for the first year. Check to find out what is included with yours. You may have enough supplies for the first season except the pre-filters, or you may need everything, that might depend on what you bought and who you bought it from.
I as a rule early in the season use 1 pre-filter each day, as the season advances, I sometimes use 2 mid-late season and a few times used 3 in very late season but that was quite rare.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.