For reference I'm interested in doing this and similar sorts of riding, for which it seems like 29ers could make a big difference.
https://deesidetrail.co.uk/route/
I know air forks are all the rage but I think I'd appreciate the relative simplicity of decent coil forks, and the overall weights of the bikes seem almost identical.
They are very similar, and they aren't decent. Generally a decent coil fork costs more than air. Most mtbs would prefer coil but it's normally too expensive and too much hassle.The solo air in the air fork is actually very good for a budget fork.
It all depends on how you get on with it, but I wouldn't touch a coil fork without it being very good. Straight away if the spring rate isn't correct, your going to be diving everywhere or the other scale have pretty much no suspension.
Either should be fine for something like the above though, aslong as your not doing it one day! Or have legs bigger than my waist

Or go full XC/Adventure type bike.