I agree with Thomas. If the weight of the body and lens together is that problematic then get into the gym and start lifting some weights to build your strength back up to a viable level to handle said gear. Train smart, but progressive. Don't train like an old fart or a girl. You want to get stronger you need to apply more resistance to a given movement over time with proper biomechanics.
I've seen a couple of responses stressing this and I shall do so as well. Make sure the tripod is tall enough for you. I'm 6'4 and need a tall Tripod. Nothing is worse than bending over all day to take your pictures because your Tripod is too short.
I have certain stronger interests that I like to take pictures of, but at the end of the day, I simply enjoy taking pictures and I'll take pictures of anything that catches my interest. If the subject matter or the surrounding conditions and environment make the endeavor more difficult, all the better. This helps to broaden my experience base and I feel helps me to become a better photographer.
Personally, that sounds like idiotic advice, geared to help you either miss or mess up lots of potential shots. I shoot a Z7 and have the same number of MP's as you do. If I was that worried about filling up a frame, I'd get my shot and crop my frame full after the fact.
When I use my ND Filters, or when I occasionally use my Circular Polarizer, the main thing I always do is not screw too tightly. I'll screw the filter on until a bit of resistance is met, then unscrew the filter maybe a quarter turn from there. I get what I need from my filter and they never get stuck. They always screw right back off.