There are only a few brands of roller skis available in the US and they are all pretty good. One particular piece of advice though, is to avoid any model with wide, soft wheels. These are used primarily for practice with classical technique; althougth, V2 does and Proski did make some skate models with that feature. The big hazard with a soft wheel is that rocks can and will, stick into them causing the wheel to jam against the frame, stopping the ski instantly and leaving the rest of you to fend for yourself.
Some will say that the harder, narrower wheels have less resistance, giving you less of a workout. But I think just upping the pace makes up for the difference in rolling resistance. Although, nothing can compare to near heart-bursting rush of having your roller ski wheel lock up on a big descent.
There are hard-narrow wheeled models available with adjustable drag devices and/or integrated brakes. These are nice features for those wanting more resistance or who might not be comfortable using possibly difficult to maneuver and otherwise potentially impossible to stop skis.
Use sturdy poles with carbide tips and no baskets. Carbide bites into most surfaces well and baskets can cause the pole to deflect off without holding.
The only protective gear I personally use for roller skiing is a pair of gloves since the pole grips cause blisters on my bare hands. I do, however, recommend using a helmet and as many pads as you are comfortable wearing. Practicing in a safe, flat area is also a good idea before heading out to that steep narrow road for a workout.