Photography

One thing to look into is whether a crop-frame camera will work for you (APS-C or whatever). The huge plus is that it, in effect, multiplies the focal length of your lens by the crop factor, so you can buy a shorter (and so, cheaper) lens for the same focal length. This is important because, as other posters have said, lens focal length is a key factor.

You do lose out on things like low light performance with a crop-frame camera, so it's nothing like a pure win, but do look into it.

If wildlife is your prime subject, especially if it's birds or shy animals, you can be reasonably sure you will always be working at the maximum focal length you have (even if its 600mm on a full frame camera), so you could look at a prime (fixed length) lens rather than a zoom one. Zoom becomes more important in landscape photos - "Fill the frame" is good advice. Photos of insects takes you into macro photography, and seperate lens from anything else you do.

Aperture - depends on what time of day you plan to take photos - if it's daytime walks on even slightly sunny days, even F11 will do fine with a decent modern-ish camera (e.g. a Canon R6). Yes, F2.8 would be really nice, but gets really expensive on longer lenses! On the other hand, photos in woods on gloomy days using F11 might still be enough to ID a bird, but usually won't satisfy due to noise.

As you might guess from the above, I've been very happy with a Canon R6 + RF 600mm F11 lens - but that met my price point.