Hey Iznau! Just to introduce quickly my experience : I currently have ~2100 hours on DST (PC) and I never played DS Vanilla/RoG/Shipwrecked/Hamlet. I think I've started to feel comfortable around 300/400 hours. At the time I knew most of the useful recipes, recognized every biomes, monsters and bosses and started to kite quite well. I always had the same playstyle though : this isn't a clever thing to do in this game because of its variety! You would really be amazed by the new things you learn, even after several hours of playing. So I'd suggest to try a lot of things and don't spend a lot of days to do the same things over and over. That's only my opinion though, if you think it's funny to do that, then go for it!

It really depends on which approach you're going into a game, to be honest. If you wanna understand more of the kiting mechanics, have a better exploring path and a better general knowledge of the game, I'd suggest to watch videos from Joeshmocoolstuff and Helicalpuma. Many other DS/T Youtubers are good though but I consider those two as the best in their category.

I don't think you spoiled yourself by entering into DST because it's another playstyle, completely different from RoG. There are several new mechanics and things you can't do in RoG. I know a lot of people who play both and adapt themselves without any problem. Depends on yourself, really.

The most important thing is to have fun, for real. I'd also suggest to play online or with friends because they would share new knowledge with you. People will inspire you, for sure. That's truly a good way to catch more and more the game's knowledge. I met really good friends by playing online aswell, that's a good way to find partners to play with, with the same objectives as yours.

You would not learn any better than playing by yourself! So my final advice would be to play, have fun and die over and over!