Feel free to get back with suggestions or comments
Are there any fees for this wallet service or is it completely free?
It's not clear to me if I can use this wallet standalone or I need to use Blockonomics merchant page.
I saw on Blockonomics website there is 1%, with first 20 payments being free, but I am not sure if that is for complete package or not.
It is open source and completely free and you are in custody of the private keys. To clarify architecture, it a webapp service layer on top of electrum wallet. So you don't need to depend on anything else other than electrum. Note that electrum internally uses
SPV servers to get blockchain dataBlockonomics can be **optionally** used to receive bitcoin to the same wallet (as blockonomics uses wallet xpub to help you accept BTC). This is just for convenience and will give you more merchant analytics and web UI (for which you have to pay the 1% fee). But this not at all necessary. This service itself is completely independent. There is no link / call to blockonomics servers anywhere in the source code