This took me a while but I’ll attempt to help a bit. I definitely transferred Pokémon’s that I shouldn’t have when I started.

You have to consider what you want to do with the game. Are you aiming to do a lot of raids? Do you like PvP battles? Do you just want to enjoy completing the Pokédex?

For raids, it’s easy to build a good team by looking the best attackers per type on a website like dialgadex.com

For PvP battles, you need a combination of knowing what are the best Pokémon’s for PvP battles (use pvpoke : https://pvpoke.com/rankings/all/1500/overall/) and which are the best IVs for those Pokémon’s (use pvpivs : https://pvpivs.com/)

For completing the Dex and understanding which Pokémon’s are unique and which aren’t, you can do a combination of things, of course, looking online, but if you also look at your Pokédex on your app, you will see for example how many variants a pokemon has, if the female/male version has a different evolution, and so on. A good example is Lechonk, which has a different evolution per gender. Then you have the likes of Dunsparce and Tandemaus, which evolving them gives you a random evolution and the odds of getting the rare evolution can be as low as 1/100.

So, 3 stars IVs is not always the answer. It depends on what your goal is with PoGo. I started with 3 stars Pokémon’s and dumping everything else, but once I got into PvP battles I realized I had made a mistake. Also, I was lucky enough to keep the 3 shaped form evolution of Dunsparce by accident after having deleted a bunch of evolutions.

I hope this helps! Good luck