This will give you some idea on inclines and the space required, I have built a few inclines and found 1:30 is about the min 'straight' incline that works- just! all depends on what you are going to run on it......
Having a deep lower track- for scenery, is not possible in limited space. That is why helixes are used but need to be based on large radii, these limit the size of trains, and limits the loco running gear life.
Down the rabbit hole.......
Eoin