I want to know if I can add erc-20 token in the exchange.
You can add any coin in your exchange. For blockchain connection however you need to have your ERC20 coin added into bitHolla Vault. bitHolla charges for adding new tokens and you better contact [email protected] for that matter.
You can add pairs and coins, just need to apply for listing on bitHolla.
As of v2 you can add new assets through the dashboard and once verified you need to donate 10,000 XHT to HollaEx Pool address.