if I take the #7 at 46th st in sunnyside, and am commuting to Manhattem, do I have to transfer?

Yes- it connects with 3 major stops in manhattan and from these transfer points you can connect to almost every other line. From Sunnyside you can get anywhere in the world without too much of a hassle.

Peeblesj is right; depends where you are going. If you need to go to Grand Central, Bryant Park, Times Square or Hudson Yards then no. You stay on the 7 until you get to those stops. However, transferring would be easier if you were planning on going to say, Central Park (where you would transfer from the 7 to the N train at Queens Plaza and go 2 stops).

Depends on where you are going in Manhattan. Maybe yes, maybe no.