Cable? Underground or above ground... maybe I'm misunderstanding the question. Were you just looking for more tips/pointers as far as best practices?
FWIW, if you find it difficult to run cable you can always go with a Point-to-point wireless bridge. It will cost a little bit but it will save the effort/hassle of running the wire (if you have POE cams you will have to have a separate POE injector in the garage for that cam).
Reducing frame rate is great until the "perp" is moving quickly etc (such as a porch-grab for a package etc) and the point at which he stops to get a clear facial picture just happens to land right between frames...
There are certainly downsides to reducing frame-rate and with the extremely cheap cost of storage, why would anybody choose to do it?
Lets consider that a well put-together 8 cam system is going to cost $1500, 4 TB of storage vs 2 TB of storage is going to cost an extra $100 to allow you to fully utilize the cameras you have (assuming you have 25-30 fps) and still maintain the same storage time-frame. At $100 extra, less than 10% of the system cost, why handicap yourself?
Considered conduit underground from basement of house to garage. Might make for easy cable upgrades later.