I have done a bit of research and found that your best bet for a multi device Bluetooth headset is the BlueParrott S450-XT which can pair with up to 8 different devices. This device has great reviews from truck drives such as yourself and have commented on using it for over 2 years without issue.
Regarding recommendations for a Trucking map route app I have come up with the following two apps.
Both of these apps offer their own neat features however Smart Truck Route seems to offer more up to date route information than the former.
We would love to hear your feedback if you go with any of these solutions, best of luck!