That devil of a question: will it be enough

I've been planning on using two Eheim 2128's for filtration rated at about 260 gph each, and then also using a Mag 350 with the micron sleeve for water polishing. Now I'm concerned on whether or not that'll be enough flow after I get everything all piped in.

I recognize that according to manufacturer's information, that's 870 gph of total flow. However, once I fill it all up with media, an inline Hydor, and inline UV, and all the bends and turns, I'm hoping it'll still be in the 500 gph range. I could be happy with that.

Just in case, I think I might build the plumbing in such a way that I could add a back-up pump inline later on down the road if I need to.

Too much to think about...