Hello Allyncooper:
In my experience the detailed map layers within Gaia I prefer most for the type of travel you suggest is USFS Topo 2016 and Public Lands overlay with the Gaia Topo, World Imagery, and USGS Topo in supporting roles. For vast overviews Open Street Map is really helpful as it provides reasonable road detail when zoomed way out. Gaia Topo tends to drop roads from view as you zoom out. The problem with USFS Topo and USGS Topo is they don’t drop any detail when zoomed way out so you quickly lose the ability to interpret what is on your screen.
If you want those layers for the western US downloaded for use without cell coverage, you’ll need a 100 to 300 gb of storage. While many Android tablets will accept micro sd cards with large capacity to augment the resident memory our experience with Gaia and those external memory solutions for large amounts of map data was unpleasant to say the least. Thus I would recommend that you get a tablet with resident memory sufficient to cover your needs. Unfortunately, that may not be attractive in terms of price - but I would bite the bullet and get a tablet with at least 200 gb of resident memory if I was starting out again.
Furthermore, I really like Gaia for a number of reasons covered in other posts. However, there is no doubt that Gaia is friendlier, more powerful, and more stable in the iWorld than in Android. We shifted to iPads and iPhones after many years of Android products primarily for the mapping and inter-device communications ability. We’re happy with the change. So if it is within your realm of possibility I would also recommend an iPad over Android for Gaia mapping. While both operating systems have strengths and weaknesses, the Gaia mapping ease in iOS is nice.
Howard Snell