By definition, ERC20 tokens have standardized smart contracts on the Etherium chain, meaning that once you do the behind-the-scenes programming to support 1 ERC20 token, there is minimal work on implementing support for all others. Like Waves tokens, a single Etherium wallet can hold many ERC20 tokens. It's not like their other payment gateways like Bitcoin, Zcash, DASH, Monero, etc which all have their own blockchain that you have to work with.