To work out the incline you need to measure the distance from where the track starts to climb to where the climb ends. You also need to measure the height the track climbs to. Divide the distance by the height to arrive at what the incline is. So for eg if your climb is 60cm and the height it climbs to is 3.5cm then divide 60 by 3.5 = 17% or 1:17. (At least I think that's correct, I'm sure someone will advise if this is wrong.)
A clever way to avoid steep inclines in small spaces is to have the upper track rise by only half the required height, and the lower track drop by half the height, thus giving you the clearance you need where the two lines cross.
I do think it's a good idea to have a removable section to your hill in case you have derailments, to allow you to clean the tracks sometimes, and for other annoying reasons which only become evident when they present them themselves (like a rogue wasp decides to build a nest in there or something ! )
