Photography

For that you should probably be looking at at least 400mm if not 600mm. The official Nikon lenses at that length can be pretty pricey, but Sigma and Tamron do make some lenses that work on the Nikon SLR 'F mount'. You can get a used Sigma or Tamron 150-600mm f5-6.3 for well under $800, they'll be more expensive new.

Not sure what tripod you have but good and relatively affordable brands are Manfrotto and Benro. Absolutely do not get any of the generic ones on Amazon, the ones with brand names that sound like bad translations of Chinese words, and that have really oddly long names like "Camera Tripod Star 700 EF (light tripod with 3-way head, photo tripod with 42.5-125cm height, tripod incl. carrying case, camera tripod suitable for SLR and system cameras), Champagne". Those things are a waste of time and money. A good tripod will cost at least $100+, if not $200+.

Sounds to me like you're on the right track!

People always think spending big on the longest lens is the way to go, and while a long lens is great, birds can often be unexpected, and zooming to close sometimes ends with cropped wings and shakey shots. 300-400mm seems to be the sweet spot for me. But work with what you have! Go find birding areas where you can get a bit closer, hang out in bird hides, crop in a bit more until you get a nice lens.

A good tripod is a worthy investment for any photographer either way.

I think a gimbal you may struggle with, birds are unexpected and fast moving and zooming in and out, moving all that glass, coupled with needing to reframe accurately will make the gimbal very hard to use.

Rather look into saving up for a new camera? Doubling your megapixels and getting built in image stabilization and better autofocus will knock anything a zoom lens or a gimbal could achieve. Why not have a look at best wildlife camera reviews, stick to a crop sensor though it's better for zooming and lighter weight gear.

Also don't forget you can rent longer lenses to play with on camera outing days and shop second hand.

I've been extremely happy with the Nikkor 200-500 5.6, especially with a 1.4x teleconvertor. I see the lens on mpb.com for around $900 if you can stretch that much.

That lens is just barely hand holdable, but I'd go ahead and grab a monopod (I have the Benro MSD46C SupaDupa, and it's great but I'm not 100% in love with it, I'd see what's good on the market this year if I were you) and the Wimberly MH-100 gimbal head. Smallest/lightest/cheapest gimbal head ever, but absolutely capable in every way. This combo works shockingly well for me in almost all circumstances tbh, haven't felt a real need to upgrade it in any way yet.

I'd recommend checking out the sigma 150-600mm lens. I think it's compatible with your camera and should give you the reach you're looking for.

Do you have any interest in going out for your birding? In which case I might recommend a monopod for a little more maneuverability and I personally wouldn't use a gimbal for this. As for compatibility I think pretty much all tripods/monopods are fairly universal.

Another option for some savings would be to find a 2x teleconverter for your camera so you can push up to 400mm. That plus some patience should get you good shots, especially if you go somewhere you know you'll find a lot of birds. Heads up though a teleconverter isn't magic and will always have a cost for that increased range. They basically only work in strong light and sometimes affect the quality of the photo (sharpness) depending on the quality of the glass.

For reference I'm an amateur photographer who mostly does birds and a little astrophotography. I'm new to this whole federated social media things so I'm going to uploading my work over the next few months. Always happy to talk photography!