You will need to be quite fit, and have lots of time on the bike previous to accustom to the position, to be able to maintain that speed 6 hours a day for 7 days, plus be able to draft well and know how to ride in a group. Not entirely unattainable I'd imagine, but training for a 5k is seriously different from training for that sort of endurance. I'm pretty sure I couldn't cope at the moment with being in the drops that long without serious back pain, but then if you have a really good bike fit and have it set up properly and are flexible, you may be different. Then again, my racer is probably heavier than yours, and a really sweet lighter bike might make it much easier to sustain.
I'd imagine your best bet would be to get the bike setup, either at a shop, or by yourself (do a bit of research, there are some good places online for a rule of thumb fit), then get out riding long rides in the position you will be riding your tour in (most likely hands on the brake hoods). If you start to get pains whilst riding, which is likely if the bike isn't quite right, you can then try to pin down which bit of the bike setup is contributing most, and adjust it slightly, until you have the bike fitted quite well - eg at first I was getting lower back pain a lot after an hour or so's hard riding, now I do have a bad back from rowing and I'm aware my back and hamstrings were quite tight - have been stretching a lot for it - but I did a bit of investigating and it appeared I could be overreaching slightly to the bars...moved my saddle forwards a little and the pain is significantly better. Little things like these will add up and make your ride much nicer if you twerk it all to perfection.
Also, especially if you are going for a fast pace, bear in mind you will need to be consuming carbs DURING the ride, not just before and after. Anything over an hour hard, and I find I need to be eating calories to prevent myself bonking/"hitting the wall". Make sure you don't get caught out - bonking and being stuck somewhere with an hour or more ride to the nearest place to get food is utterly horrible, it will be the longest hour of your life.
Related, doing lots of long, low intensity rides will help you adapt towards burning fat as a fuel more efficiently, which will help a lot with sustaining the long days. I remember reading a study that suggested hard training when already in a glycogen depleted state significantly sped up this adaptation over just doing lower speed endurance training, like go out for an hour a long time after your meal, and when already pretty depleted, start doing medium intensity intervals (something like 5mins at a time or something along those lines, not short sprints, slightly longer concerted efforts) for a bit. I can't find it at the moment though...which is annoying, so perhaps take this with a pinch of salt, and I'm not sure it was a particularly big study.
Anyway, what you are suggesting seems good, ultimately you just need to do the miles and get used to being on a bike for that long.
Otherwise, just make sure you carry spares and tools with you, it sounds like it'll be a really enjoyable ride, have fun both on the ride and training for it
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