I have used Nikon since I went digital in 2009. I started with a D5000, got a D5100 about 2 years later when it was released. Both are good cameras and the D5300 is a step up from those. It has the same sensor and focusing system as the D7200 which is an excellent crop-frame camera.
The kit lenses are quite good quality, I had the 18-55mm and 55-200mm option and got some great results. I also had the Sigma 150-500mm which was a good lens for its time but has now been far surpassed by the newer 150-600mm Sigma and Tamron Mk2 lenses.
I would recommend that you go for the D5300 with the 18-55mm and the 55-300mm lenses then tell your bank manager to stand-by because you need to loan 16K to get the Tamron 150-600mm Mk2 lens
Nikon used to offer a free photography course when you bought one of their entry-level cameras, I'm not sure if they still do but it would be worthwhile going on a course to get the basics of photography anyway.
Wildlife photography can be one of the most frustrating pastimes there is but the rewards when you get "that shot" completely outweigh the irritations.
Welcome to the nuthouse and to the photographic fraternity!
Hunting cannot be considered a sport as all contestants in a sport should know they are playing the game!
.... Jj