I am currently in the process of converting an old Pearl Export into an electronic kit. I won't recommend you do that unless you have 3 weeks of spare time, lots of tools and like to DIY

, but here are some thing I've learned in the short time since I decided to get an E-kit:
Roland is great, but insanely expensive.
Don't always expect pads and modules from different companies to work well together (they will *work*, but not well).
Most of this stuff is seriously overpriced! It sucks, but it's the truth. (you realize that when you see people building better stuff than Roland can offer for 1/10th the price. If you don't believe me, head over to Vdrums.com DIY forum ).
Your questions:
-if it will be triggering SD2.0 would he need to invest in a drum module?
You need an interface to connect the triggers to your computer, i.e. triggers in -> Midi out (or USB connection). I'd say get an Alesis TriggerIO, it's the cheapest option, and a relatively good one. IF you do decide to get a big $$$ Roland kit, though, buy a Roland module!
-would there be much lag if we run it off of SD2.0?
That completely depends on your audio interface. It is not the software that determines latency, it is your hardware. What kind of latency can your computer handle? Only way to find out is to try it. (FYI: Most interfaces today are pretty good, even my Behringer UCA202 gives me 64sample latency at 48Khz on my 2 year old Lenovo X200)
-what would be the best deal?
It depends on who's going to be playing the kit. If an Alesis USB Studio or an Alesis DM10 is enough, then get that. But if the player is unsatisfied with anything but the best (meaning: it feels just like an acoustic kit) you may end up having to drop 5 grand on a Roland TD30 :/
(of course, if you do it yourself you can build a kick-ass kit for less than a grand, but it takes skill and time)