Some questions.

Hi there I just started playing and I have a few questions.

I feed my 1 star monsters to my 2 star monsters, but now I have about 40 2 star monsters , and 38 of them are level 1. should I just feed them to eachother?

Also what do I do with the 2, 3 and 4 star units I dont use? I have about 10 4 star units and I'm not sure what to do with them.

Is there like a ranking for 4 star units to see what ones are the best because I leveled most of then atleast a little so it's very hard to compare what ones are te best.

Thanks in advance!