Hi Mickvp,
Hopefully I'll be doing a similar trip this year. Will no doubt just look out for a weather window opportunity.
Regarding phone charging, I just have a handlebar mounted cigar lighter socket and use a plugin usb converter to charge the phone or powerbank, these being placed in my tankbag, which is also handy to have for maps or route notes etc.
My mini compressor would work off this socket in the unfortunate event of a puncture. Spares wise just bulbs, chain lube, and on a long trip sometimes include the rear axle nut socket with a suitable bar in case chain adjustment necessary.
Pack your clothes in a bin liner/builders sack just in case your waterproof luggage isn't
. I use a Lomo top opening bag to fit all my camping stuff in. You'll also want a chair of some sort, the Helinox copies are good and take up little room.
Pre trip maintenace is really just standard stuff that you'd do anyway. State of tyres, pressures, oil, how old is the brake fluid, what's the pad life. Stuff you normally keep an eye on. Lastly pack your bike a day or so before you go so you'll know you're comfortable and have an idea of the increased weight. Good luck, ride safe.