Is there anything particularly to look into to know if a wallet is closed source or open source? I'm tired of people saying the difference but not how to identify a closed or open source wallet.

Among huobi wallet, trust wallet and Atomic wallet which is the best for a newbie that wants to buy some altcoins? I did research and it says electrum is the best mobile wallet but no electrum for altcoins.

Can you buy rx580 for 340$ today?