1.  Ranks can be seen by how many stars each champion has on their profile image.  Doomscreech here is Rank 3.

2.  Rarity is irrelevant with regards to rank.  Every rarity can be ranked up all the way to 6*, though they do each start at a different base rank.  

1* Common, 2* Uncommon, 3* Rare, 4* Epic, 5* Legendary 

3.  Which champ should be ranked has little to do with their initial rarity.  It's dependent on your account and what you need at the given time.  Starting out Artak and your starter champion will likely be your 1st 2 rank 6 champs, unless you get lucky with champ pulls.

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