New Player - Custodes vs. Dark Angels and Black Templars

Hey all, getting back into 40K and was hoping to get some perspective. I picked up the Custodes combat patrol but want to get a SM army going as well. I'm trying to decide between Dark Angels and Black Templars, mostly because I used to play SM long ago. But, as I'm learning more about both, they seem very melee focused (certainly the BTs and DWK lists for DA), and I know Custodes hit like a hammer in melee. So my questions are:

  1. How similar are Custodes playstyles with DA or BT? They might all have strong melee units but am I oversimplifying to say they play the same?

  2. Are Custodes simply "better" versions of the SMs (talking gameplay, not lore)?

  3. Will playing both Custodes and DA or BT have enough "freshness" or will it feel all the same?

Thanks!