Been doing 3 times a week, but trying to decide if i should do more. Doing 50 pound pack 1 to 2 mile hike depending. Going to extend this over time.
Well since it is important I will ask, what terrain are you hiking? Road is easiest, trail is more difficult and bush whacking is harder. Next is pace, 2mph or 4mph? 50# for 2 miles at 3+mph cross country thru thicker areas with lots of up/down (I understand we are not in the mountains) is a huge difference compared to 2 miles at 2 mph on a road. We have some trails around here that are up/down more than others but going straight thru the woods (no trail) is more difficult imo. Even a strictly deer trail is much harder than a hiking/horse trail.
I love a nice hike but if I am working toward a fitness goal I am generally doing shorter/intense workouts, doing simple tracking of what I am doing and gradually increasing frequency, pace and difficulty.
I think you will see more cardio gains thru increasing pace and difficulty than by increasing distance.
I would also seriously consider posterior chain free weight exercise's like azz to grass squats, deadlift, smith machine leg press, glute bridge, clean and press, etc.
Swimming is awesome and is also going to be more beneficial with increased pace/lap speed.
As far as too hard too fast:
General rule for me is that if I am looking forward to the end at the end of a workout I am right on track, complete exhaustion at the end 3-4 times a week is not good for me but I am older.
If you can run then I would run some.
Keep at it, brother......looking forward to seeing you for some whitetail action this fall. I may go up to Caulker City for a camp out and some hiking in a few weeks if you want to meet up let me know. Thinking about getting out of Lawrence permentaly and need to look around the state for some living options, going to start in the north centsal region.