Apart from the factors you mentioned, I think its also very crucial to check the settlement process. Not all merchants want to hold cryptocurrencies, especially the volatile ones. So when I chose Capital Wallet as my payment gateway I also checked these - what settlement currencies are available, if payments are auto-converted into the desired crypto or fiat, the conversion rate, the time it takes to get funds in your bank account etc. Gave me the much-needed clarity in decision making.