Need some advice, Ty in advance for your replies

「ph」panda

Im a newbie in this game and I read a lot here in forum because I also want to be good in this game,

1st
I currently have Lunaria, Shall I Change it to Nyssa? or save my stars for Electa or Armora (which is better) , then up to which point shall I continue and stop then save for higher tier, What are the good Angels?

2nd
I currently have ;Zweihander, Rose knight , Pyrona , Atlanta , Demon Hunter and Djinni
Which of this are good combination in arena?;
I also would like to know whos the best line up, Some say Zweihander, Palandin , Pyrona , Earthshaker and Night Sentinel

3rd
I would like to have Paladin too and Earthshaker, any tips how to get them?

        4th;
I have read about spending on diamonds, whats really the best way to spend diamonds?
Is it good to open 10divination for 4999 gems as a free user? (some say its not because I might get just crappy 1 or 2 star heroes that I might dont need)

Thank you so much for your replies,
more power to you guys

IGN: XPRNC
Server: Forsindil (UK2) new server