Oh wow, that looks really fun. We have trails going through forestry here too but not as long as that! I need to get out more and see if there's some better ones near me.
For the boots, I've been using an old pair of Fox that I've had for almost 10 years. They've held up all this time so I guess I can recommend that brand, haha. My approach to buying gear is to get on the Cycle Gear and Revzilla mailing lists; wait for a sale/clearance, and pounce on it. I like Cycle Gear in particular because there is one near me so I can try before I buy.
Oh and on the GPS, I bought this phone/GPS mount back in 2013, I use it with my phone. It was cheap and has been holding up well. Not waterproof but I've been drenched a few times and the phone survived. You can kinda see it if you zoom into this photo. I use the Garmin GPS app, because google maps eats up data and doesn't work when there's no cell signal.
I have the same one. works great, just can't support the bigger phones/gps screens