don't go for a 45, it doesn't look steep on paper, but it is and it doesn't help out, all of the speed you build up will be lost in the transition and personally I felt less comfortable with that loss of speed, over a gradual gain/ loss.
8 feet is perfect for flat ground, you could easily get away with 6 if you are on any kind of slope.
To save it from being 23 feet long raise your tranny and have less of a jump, it also help to save on speed. In other words you don't need a 2 foot tall jump for a 2 foot rail. Mine is set up for about 1.5 foot rails and the difference between flat and the top of the lip is only 6-8 inches, but my flat section is about a foot off the ground.
My flat section is only about 1.5-2 feet long, as well as my 2 other transitional stages, any longer and you will loose too much speed I find.
For transitions think of it as how people used to make perfect curves in line rider or geometric drawings
I more or less set my design up on a grid to figure out where the intersections would be and lengths of each piece of wood.
For your set up as is I would cover at least half of it in latice or I don't see you making it to the end. I've been there and it's not fun realizing after 3 hits that it isn't going to work.