what to buy that is not too complicated to start with
Hello Nicky, I think everyone's down the pub.
Most camera bodies that take interchangeable lenses might fit your brief. They're all pretty good these days.
I think you might consider bodies that have the sensor formats 'Micro Four Thirds' and 'APS-C' (aka 'Crop', which the D3500 is). And get your hands on a camera (or two) to see how it fits your hand and how you like the viewfinder experience. The final thing might be the controls and menu structure, but they might be hard to assess from the off, so maybe leave them aside for now and take them on trust.
Nowt wrong with a D3500 for your purpose! Most camera bodies come bundled with a general purpose short-range zoom, which is ok - for general purposes!
Wildlife, however, is (or can easily be) a bit more specialised. For close-ups of plants / insects, a 'macro' lens is best, which might have a set focal length between 50 - 105mm, for instance. You can use it for general purposes too, but it doesn't zoom.
But for birds, you need more reach, thus a telephoto, which might well be a zoom. The greater its zoom range and the longer its maximum focal length are, the bigger and heavier it'll be, though.
Thus you could buy a camera body and ultimately have two lenses -a macro and a tele zoom. But maybe you don't want a macro to start with? Because all that's likely to blow your budget big time anyway!
So I'm just pointing at directions of thought, not being prescriptive. I can certainly recommend buying used from reputable sources, and this'll help the budget loads - a five-year-old camera won't be far behind in technology terms.
) It's what lens you'll need to obtain a decent quality image of your chosen subject - something over 300mm would be my suggestion - I would avoid the 70-300mm lenses IQ is nowhere as good as a say a 150-500mm or 150-600mm