Hey Gian!
I grew up in Ferndale and did my first tour in the U.P. I have to say that the further north I went in the state the more I liked it. Went to school in Ann Arbor, and although the mountain biking is lots of fun the roads kinda suck. The U.P. Still has a lot of wilderness feel and good shoulders on all the highways (that I´ve been on). Pictured Rocks and the Keeweaw are amazing. Even up in the fingertips is lot of fun. Just know to avoid the little tourist highways when the RVs are out (like in the Traverse area). There´s a lot of state parks and stuff that go from Pontiac in an arch towards Jackson (I´m pretty sure). Maybe ride to Hell? Hit up the Potowatomi. For buying gear there´s an REI in Troy (I´m guessing you´re kinda close to there?) and although it can be more expensive if you don´t like the gear you got after you test it out you can take it back for a full refund. That´s what I did after my first few tours to upgrde to some sturdier stuff. The Troy store even let me use their tools to put my rack on when I bought it.
I love my pocketrocket when I´m touring or backpacking in the States, otherwise it´s impossible to find fuel. You won´t be dissapointed, and you can use the SnoPeak fuel and everything that has the screw-on interface, the MSR fuel is most expensive.
The only upgrade I´d make to a mountain bike is to buy some slicks. Head to your bike shop (or REI if you´re already going) and ask for some 1.5¨ or 1.75¨ tires that can handle at least 55PSI. I bought a pair of Bontrager Special K 1.5¨ slick down the middle, little tringe bumps on the outside with Kevlar protection almost 6,000 miles ago. One of my best investments.
Don´t forget the long layers for the bugs! Stay visable! Michiganders love to drive fast. Don´t wear any Scarlet and Grey, UofM football has been struggling for a while now...
Have Fun!! Say Hi to Michigan for me!
-Donal
p.s. Forest Service land is free camping so long as you´re over 300 feet from the road.