Upgrading the family camera - need some advice
Hi, I'm an avid hiker that's been using the family Canon EOS 4000D for a few years now, with the base 18-55mm lens (for landscape shots) and the EF 75-300mm III (for wildlife) that my dad bought almost 8 years ago now, together with the camera. I frequently switch between the shorter and longer lenses during hikes, as I really like capturing both landscape and wildlife pictures. Even though I'm a student right now, and finances are not unlimited, I've been thinking about upgrading my setup. I'm just not sure in what order :) My main "problems" right now are general unsharpness at max zoom, slow and unreliable focus, and the resolution of the pictures not quite being high enough to use them as backgrounds for my PC.
I've been looking around, and think a good upgrade would be a 70-300mm IS USM II zoom lens instead of my 75-300 I have right now, due to its fast focussing and (apparently) general sharpness increase? I can find these second hand for around ~500€, and if I sell my old 75-300 I might recoup about 150€.
Another option is upgrading my camera body, and I think a Canon EOS 90D would be a good upgrade, coming in a bit pricier at ~700-800€ secondhand. Again I would be able to sell the 4000D, recouping ~200€.
I think I want to eventually do both upgrades, but there'll have to be some time between them to save some money. What would you guys do first? What'll have the biggest impact? Would you guys go another way with other stuff?
A last option would be the 18-135mm lens, giving me a bit more flexibility between landscape and wildlife photography, not having to constantly switch.