W245 cable run

[Gollom]

I am fitting rear PDC and the cables come up in the auxiliary battery (that what it is?) compartment. I intend to route the power cable to the fuse box under the offside front footwell. Anybody done this - if so was there an easy route through the car? (hate re-inventing the wheel!) Or is it a matter of trial and error?
I am going to use one of these - can I just plug it in any empty fuse slot? Plus what size fuse would you suggest?



Many thanks as always