Tell us more about your tour -- that sounds great!

You absolutely must try on shorts. There's really no other way to know if they will work for you. It seems like shorts are a lot like saddles -- everyone has a different preference. Unfortunately, spending more generally does get a better short. I found a great deal on Castelli Visio shorts recently and I really like them -- it's worth checking Nashbar/Performance for good deals on PI shorts (which most people either love or hate -- personally I'm sort indifferent about them). I find Shebeest SSS shorts very comfortable too.

Miscellaneous things that may be useful:
--arm warmers, for when the wind kicks up or it's chilly in the morning but warms up by noon

--a very lightweight and packable jacket and/or vest, like this:
https://shop.sunrisecyclery.com/item/14736/
http://www.rei.com/product/759783?pr...:referralID=NA

--definitely gloves

--seat bag and flat-changing stuff, if you don't already have them...

good luck!