Switched accessory fuse box

[P156KWJ]

I've got a couple of additional electrical accessories that I've installed in my S40 since buying it last year, namely a hardwired dashcam and a homemade bluetooth/FM modulator. Currently these are running via fuse taps in to the electric window circuit and the radio circuit fuses respectively.

As I plan to add an accessory socket that will run to the boot somehow at some point, I'm now getting to the point where I don't think it's wise to carry on adding fuse taps willy-nilly as I don't want to damage any wiring (or cause any fires) by inadvertently overloading a circuit. Also of course there's only so many you can add before you run out of room. (I'm aware you can install fuse taps the 'wrong' way around to run the fuses in series thus protecting the feed, but it's still not ideal in the long run).

My questions are:

- Are the stock alternators fitted to the 115hp 1.9D suitable to add an additional cable directly from the battery with a maximum load of say, 40-50 Amps at most, so I can install a new accessory fuse box in the cabin somewhere? Are there any other considerations to make such as affecting strain on the battery?

- Is there any easy way of making sure the new fuse box only draws a load when the key is in step one or ignition, by means of a relay?

Thanks in advance!