The reason deisel trucks have such huge intercoolers is because a) they run much higher boost pressures (25+ psi) and b) the turbo stays in some sort of boost more of the time, especially when hauling, both of which generate quite a bit of heat. For a low boost application, 5psi would be ok without one on a blow thru setup. Many have done this no problem. However, any more than that you'll need an intercooler. Personally, I don't see why guys go through the process of building a turbo system, and then not use an intercooler. It's not like 10 years ago when you had to drop $400 on a Spearco, a decent unit can be had for 100 bucks on ebay.
As for the dual inlet on the turbine, that's just to help the turbo spool faster.