The 50mm lens as pointed out seems good, but I'm not sure if when you do the math, that the 50mm lens will get me as wide of a shot to capture more space than a stock HF100 (it seems it's worse?). If not, I may just in fact get it, even though it's a Prime lens.
50mm Will not be wide enough. Trust me. That's one reason why I don't like when people recommend that lens to a new user. That's why I always say go for something wider like the 30mm or 28mm. If you want even wider then you might want to start with the kit lens although you won't have a very goood DOF like a prime lens at f1.4.
To answer your question yes you can control the blurriness but the more the fstop opens the better the blurriness. DOF.