I’m new to biking as well, but from what I’ve learned, offroad-bikes are usually quite low in insurance, might suite you nice since you were keen on mountain trails and such. And people riding them seem to be pleased with their touring/commuting abilities.
As for gear, I’d go with over-pants with zippers down the sides, you make it sound like interstate speeds are a walk in the park should it come to an abrupt landing, well it’s up to you wether how much you treasure the skin on your legs really. (Imho, if you plan on keep riding for life, it’s a question of when you crash rather than if, and you can do much to affect the outcome)
welcome to the forums btw!