if you're not on well water i don't think you need R/O. of course i'm sure that there are old buildings and shitty municipalities with bad quality water, but why strip out the calcium in your water just to add it back?
The real question you should be asking yourself is, "why does the PPM have to be at 1000?" feeding is going to vary a lot on genetics and plant size. Why don't you just start at 1000 ppm total, and if your plants are yellowing or look like they need more nutes after a while, feed em more.