[bigeasy1]

You can mount the blower anywhere, and as you said, run the hose down to the bilge.Try to keep the hose a bit off the bottom,as you don't want any debris or bilge water to enter it.

The original blower on my Tsunami,was on the transom,just above the engine with the hose from it dropping straight down.
The vents you have will work ok with the blower on.You can always leave them the way they are,and put another one in facing forward.
It doesn't have to be in the same spot,it could be anywhere,just so it will send air towards the bilge area.
Don't lose sleep over it,it's not absolutely necessary,as long as you have the two vents in the back,and the blower setup does it's job you'll be ok.