Joe,
What kind of track are you planning on using? While code 250 aluminum as I use requires good support a heavy track like code 332 brass will bridge a considerable gap on its own.
My very first outdoor layout used LGB code 332 brass track and had no supporting roadbed at all. I secured blocks cut from PT 2x4s (approx. 2" long) to the bottom of the track sections about 8" to 9" apart and 3" blocks at track joints secured with brads through the ties. This raised the track to 1.5" height and the heavy rail easily bridged the gaps between blocks without sagging Ground cover pretty much covered the blocks and of course ballast can also be used for a raised roadbed look.
The track was simply set on the ground and the only grading needed was to smooth and flatten the area beneath each block being sure to watch that the track was laterally level. Regular LGB rail joiners were more than ample to hold the track together and with the joints liberally coated with black conductive grease gave good current feed to the track as well.
Like your area mine was pretty level and only required eliminating a few humps in the ground. The layout was down for 4 years with little maintenance except the usual track cleaning (one incentive for battery power) and clearing apples off the track.
Cheap and easy and it works provided you’re using 332 rail.
And BTW: no concern about curves either as the blocks secure to the bottoms of curves and switches as easily as to straights.