I have run the 650 for a couple of hundred miles (1 week!) So I am not what I would call an expert on them, however Adventure riding is just a state of mind really and low key low cost journeys are often the best (My favourite memory is Scandinavia two up on an ill prepared T595)
I reckon the 650 is all but bomb proof and should be the least of your worries
As the others say, screen and seat are hugely important, I would not go too high with a screen as it is easier to break in a spill, but it is essential for keeping the elements off you. I always use a sheepskin cover for long journeys, my choice is a cheapy rug from eBlag cut to size and held on with elastic cord, it is worth an extra 200 miles a day and just works.
The bike needs to be mechanically sound and carry some essential spares such as bulbs, oil a couple of plugs and spare chain links, more if you are away from sources of BMW spares. Carry a puncture repair kit, pump (CO2 is good as well) and tyre irons. Tourances are good for a lot of things and last for ages however if you are doing big distances think about what you will do when they need replacing.
Engine bars are handy but I always think DFC!
Panniers - TT are good but pricey however the add mechanical protection to legs and bike and you can gets loads of gear in them. Fit locks. I always use a tankbag, good for carry away stuff and spares socks, gloves, some cash, MP3 player and maps.
BTW - panniers make great tables and chairs.
Then it is just down to what you carry, a small tent keeps the bugs away and the rain off your head. Camping - keep it light, I use a 1/2 season down bag as I have no plans to camp at the base of Everest, a self inflating mattress and repair kit is well worth taking and as a luxury take a travel pillow.
I always cook on petrol using an MST Dragonfly, handy because the fuel is always in your petrol tank and it also means you carry a couple of litres spare in the cans. Carry lots of water and assume the shops will be shut at some point so carry some food, I like MRE's but that is just me, I also carry UK teabags
Take a couple of small LED torches, the Inova X5 is very expensive, but indestructible I also have a small LED leadlight I made up and keep in the tank bag just in case.
Two pairs of gloves are essential and in heavy rain waterproof over trousers are handy even if your gear is waterproof.
Just get out there and enjoy yourself
