the additional fuse box will make it a cleaner install and enable you to do everything that you want. There are several options available. I used a Centex ap2, other use a deep blue, there is an option from some yankee in japan ... eastern beaver etc etc.
I wired mine directly to the battery, then there is the option of triggered (using relays) or always on 'lines'. For example, and like yourself, I wired my satnav to be 'always on' when the ignition was turned. My spot lights were however triggered by my lights via a relay. I included other options such as a USB charger, usual car jack plug in sized thing (for tyre pump) etc. Fairly easy to install, and you kind find many detailed writeups here and on advrider.