@nuke_diver I haven't really ridden up in B'ham much. From other parts of the PNW I have ridden, on the west side, I would expect it to be a bit rooty, and slick if wet. Wet roots are sketchy. Not where I would take my gravel bike.
Smooth, loamy or firm, single track can be nice on a gravel bike. But I have no desire to ride a gravel bike on anything very rocky (not gravel, I mean rocks that can tend to bounce you around) rooty, slick, etc. I would want my mountain bike with it's big, really knobby tires, and suspension for that.
As far as direction on trails, it depends. Lots of "bike parks" with prepared banked trails with jumps and stuff flow one way, and often are designated that way. Especially if the jumps require enough speed to clear, which often means you can't see what is on the other side. General single track trails that are open to bikes are often two way. There can be trails in between that are somewhat prepared, but also are used two ways. Lots of the plain single track that were not specifically built for bikes can be a bit steep, such as you say 8% for a couple miles or whatever, as they weren't first cut or built for bikes. I used to try and clear everything, but now, I am just making sure I get out, and if I have to hike a bike for a little bit, but am still doing it, it is a win as far as I am concerned.
I would think there would be signage if the trail was one way. But of course, and I know you know this, know before you go. Find maps online, call one of the local bike shops, the local Kona guys at their in town shop are nice. Likely they will be glad to answer questions you cannot find answers to online, and may be able to direct you to other trails. I always love to check in with bike shops. Normally in person, but, we are in strange times. I bet you know this stuff too, so don't mean to state what you already know. But that is what I would do.
It is not as good as a purpose built expensive smart trainer, but those are really expensive and take up a lot of room. If I get a used power meter crank, I can connect that to Zwift too for better accuracy as opposed to the calculation they do using your cadence and speed sensors on this bike. Thinking it will be good for my riding, especially for over winter.
