Just had a quick look at the two systems on the page you linked to since I was curious about the 3 DI stages. The last paragraph of the system description confuses me.

"STAGE 5, Stage 6 and Stage 7: (Demineralization by Ionization DI Resin Bead Filtration)
Resin Filter / Demineralization by Ionization– Removes hard water minerals through an ion exchange process. Intended to prevent hard water scaling and staining on the R.O. membrane that are caused by inorganic calcium, magnesium, and soluble iron. Greatly increases the working life of the membrane."

If these are indeed stage 5, 6 and 7 (meaning they are plumbed in after the RO membrane), how can they extend the life of the membrane by removing the minerals described in this statement? If one or more of the DI stages are plumbed in before the membrane, you'll be replacing DI media (not cheap) like nobody's business (depending on the hardness of your source water). So yes, it may increase the working life of the membrane, but you'll be paying through the nose replacing DI media. Probably be more cost effective to get a more conventional system and replace the membrane every two years. Several other things worth noting on the Aquasafe systems is that they don't have clear filter housings for the pre stages and all the DI stages are horizontal. I believe a vertical DI stage is more efficient.

In Richmond you shouldn't need DI so I would avoid it all together since it'll just add cost to maintenance with little gain and it's a pain to change.

If you do go with DI the one will be more than adequate but you can go with three if you're planning on failing behind on filter changes as the extra DI will help.

For drinking water just tee a line in before the DI to your faucet or whatever. Just be sure to also have your pressure water storage tank also plumbed in prior to the DI. Also if it has a final polishing filter use that only on the drinking line.

Also keep in mind if it's not much more to add the three DIs you can get that system and remove all or some of the DI canisters and add them later if needed or use them for quick changes.