I have a 3.4% grade on my mainline, along the back fence. The approaches are all level, and the grade is on the straight track. I need more locos to pull long trains, but MU operation and doubleheading is fun.
To complete the mainline, I have a big long 40' section of downhill that is 5.5%. It's steep, but works well. I can run short trains up it also, like 10 cars.
Nasty grades, but workable. I think I saved myself by not having any of the grade on the curve.
Go for it.
Regards, Greg