Yeah the Dry is the nicest time for Southerners to visit. There's awesome fishing most of the year, pelagics are the go in the Dry, sight casting to schools of Longtail tuna busting up in the bays, trolling for Spaniards. Listen to the Tales From the Tinny podcast for lots of Darwin Barra-centric fishing info.
I think riding in the Build-up or the Wet probably warrants an eBike ! You get sweaty AF just standing around outside
NT is an experience all by itself. What's more, one of the local trail companies up here just spent a whole heap of time developing those trails. Katherine is a little harder to get to (fly into Darwin, drive down) but well worth the effort.
Watch out for the big lizards in the gorge though...
I spent a week camping, bushwalking and swimming in safe waterholes (under awesome waterfalls)1.5 years ago around Catherine and similar areas. It was an awesome place and I could see a lot of awesome spots for trails with cool rock features. I suspect there would be a bit of resistance to anything technical or challenging going though due to the remoteness and distance from hospitals (the number of people that get lost each year would put them off as well)