I bought a 6 year old house with a State Select PR650XCVIT with a 2" vent, and have a few questions about the installation.

1) It say the termination must be a 2" T or a 3" 45 elbow. Mine comes out the wall, has a 45 elbow and a foot of 2" pipe. So it is not right, but it is hard to see why it matters. Does it?
2) It says to be a minimum of 3' from an inside corner. Mine is 4". Why does that matter?
3) I have 1' of 3" pipe, a 3" 90, a 3-2" reducer, 1 2" 90 elbow, 4 2" 45 elbows, and 20' of pipe. The maximum pipe is 35', each 2" 45 counts as 2.5', each 2" 90 counts as 5' and a 90 counts as 2.5'. So I figure it is 2.5' too long. 20+(7*2.5)
It seems to come out pretty vigorously; is it likely to be a problem?
4) Can I reduce the effective length by increasing some of the pipe from 3" to 2"? I can move the 3" to 2" reducer about 8' further down, and change a 90 and a 45 from 2" to 3". I can't change much more because it isn't very accessible.
5) On the outside there is a 2" 45 and 2' of pipe. It would be easy to put a 2-3" reducer there and change the pipe and the elbow to 3". Is that okay?
6) If #4 and/or #5 are okay, can I extend the outside pipe to get it beyond the inside corner? It says the termination must be as close to the house as possible, but can I make it longer if I insulate it?