ERC20 Tokens doubts

[Alex Brend]

I have few doubts regarding ERC20 tokens

1) Any good apis for ICO price ticker? Like idex.market https://prnt.sc/jbz4v5
2) How does idex.market able to sell token to users? Do they buy the ICO first to their wallet address?
3) Lets say you create an app which reward user with bounty. Example if user vote something, he will give you token. I have to write the vote logic in solidity? Or I can write this in php / nodejs and just write token transfer code in solidity.