My very first "adult" bike was a Cypress. Its stolen now, but I still remember her well. I would NOT commute 20-30 miles on a Cypress, simply because of the poor shock... I could see the bike pogo-ing up and down with every pedal stroke, especially under high load. Pretty much ANY bike can hop off the occasional curb, although if you plan to make that a part of your regular commute a suspension fork would make it easier than most. The question I have is thus: if you're already going 20 miles, is there no way you could go an extra hundred or so feet to avoid having to jump off a curb? It'll save your wheels a lot of wear and tear, suspension or no suspension.
1. Rapid Fire vs Twist: Typically a matter of preference. My Cypress had the twist shifters, and I loved them. I find that even cheap twist shifters can be made to work well, given that they're basically two notched composite rings clicking against each other. The micro-indexing on the front shifter comes in handy for dealing with chain rub, something Rapid Fire shifters don't do. On the other hand, the Rapid Fire shifters will be more consistent/precise when shifting the FD.
2. The basic Cypress comes with a "Mega Range" FREEWHEEL, not cassette. There two issues here. First, you're up a creek if you want to upgrade to most 8- or higher speed systems in the future, which all use cassettes. You'd have to replace the rear wheel/hub (on the other hand, 7 speed freewheels are very cheap these days). The other issue is that a Mega Range FW is basically a six-speed 14-24 FW with a final 34t cog glued on the end. This means there is a huge jump at the bottom of the range, which basically makes the 34t a bailout gear (14-16-18-20-22-24-34). The PG-820 is configured a little more closely, and goes 11-12-14-16-18-21-26-32. While this spacing still has a lot of big jumps near the low end, the range is more even, which means you'll have an easier time picking a good gear if you are going up a hill, since the largest jump you have to contend with is 6 teeth, not 10.
The other differences between the two bikes I noticed is that the DX has a slightly nicer crankset, and the tires are marginally nicer. If you can get the bike shop to order a DX for you to TRY (without putting any money down), you should take both for a test ride. The differences between the two bikes are subtle and probably more a matter of preference, so its impossible to say which is better when one considers the $100 price difference. Good luck.