Hi Jamie!
Welcome to the club! I very much encourage you to work 'with' the garden and its features than bulldoze. This worked for me when I lived with my (now) ex; = her garden + house!
Tracklaying: quite easy, if you want anythiing more durable than a few weeks I strongly suggest you lay it onto planks of wood, best is probably decking planks, and nicely wide - either side of the track 1inch cos the growth of lawn + other little plants will make you cut it every 2wks!
track on left on wooden plank, not wide enough! Other on right crewed onto slabs, or laid on some cardboard I pulled from a skip...
track is screwed onto slabs as kept sliding sideways:
wooden plank underneath, crossing lawn level so lawn can be mown easily by SWMBO!
PLease ignore the helper! Here crossing via bridge in front of the allotment, behind compost bin, past apple tree (bent to left) to reach in forefront flowerbed (on planks):
Pond needed extra solution planks on wooden pillars as also had to rise considerably (garden on a slope):
Choc block with goods train, again crossing lawn level on 'buried' plank:
Station is also on cardboard, although that disintegrated after 2years! Here b4 filling with ballast, again ignore the helper:
and after filling ballast: