Moving a toilet (with a flat vent)

I have a toilet that I am attempting to move from one side of a wall to the other. The current set up has a drain running up the outside wall of the house from the basement the drain makes it to the second floor bathroom where it turns 90 and runs parallel to the floor for the length of the bathroom then turns 90 and head out the roof. (See the pics) If looking at the wall the drain is nearest the toilet was at the right side (about 3 feet from the 90 that turns and heads out the roof). I want to move the toilet to the left beside the outside wall of the house) I have been told that I would be creating a flat vent (and I am assuming that I have always had one) just now the length of the vent is more like 8' before making its turn to vertical (compared to the original 3') I have added a few pics below that show what I am working with.





I have a few questions.

1) Is it ok to have a "flat" vent this length?
2) If not... what size vent do I need?
3) Does the new vent need to be before the new Y or can it be after?
4) can I put a T in the 3" pipe and run it at a slight angle for 3 or 4 inches towards the wall then up between the studs of the wall in the Pics?

Thanks for all of the insight

Out here the inspectors don't allow any flat vents. Although, the fact that your flat vent is 3" helps to keep an air flow in it, even if the drain backed up and some waste was left in the vent section. To vent it to code, you can put the 3" x 2" combo(tee) in the line before the new 3" wye (wet side) and run it to the wall on a 45 degree angle, then vertically up the wall.

Helpful Plumbing Hints for Residential Construction by Bert Polk Plumbing Inspector Lincoln County