Grades

Do you want the grade to go high enough so that one track crosses over the other? If so, that's going to be very tough to do in your space with only a 2% grade.

In round numbers, a 2% grade rises 1/2" in 24". To get to a height of 5" (the minimum clearance needed for an overpass) at 2% will require a run of at least 20 feet.

In round numbers, a 4% grade rises 1" in 24". Increase the grade to 4% and you cut the grade distance to about 10 feet.

Another thing that can help:

Lower (Dip) the bottom track as well as raising the upper track.

Still not easy on this size layout.

Also, don't forget, you can't just snap to a grade, you have to ease into it, this adds several feet of length to the effective grade distance.

im thinking not crossing any track over each other because of the low height and minimum slope and size of the plan.

An alternative is to keep the track level and vary the terrain around it.  Under cut, build hills, tunnel through something, use a backdrop.  All of those tricks give the appearance of the track changing height without any substantial change.  You could even vary the track level a small amount but change the surrounding terrain to a greater degree.  All of that fools the eye and makes the look far more interesting.

Or you can just keep them separate loops, you will still have plenty of train running action this way.

Not sure what you're after. but here's a 5x8 that could be expanded a bit to get the grade below the current 2.6%.

Informative thread on Figuring Grades.   Interesting to note that my grades are 3.8%. It takes close to 14 ft. of run to get a 6" rise. 

What percent grade does a Lionel graduated trestle set make in 0-gauge?

The Lionel 110 trestle has a change in height of 1/2" from pier to pier in the middle away from the transition. It goes to a height of about 5". If 10" length pieces of track are used, the grade would be 5%. There are 24 pieces in the trestle set, 12 to go up and 12 to go down.  So it would take 10' to get up to 5".