Currently you can pay with the ICP and GHOST currency that is available on all CEX exchanges.
ICPSWAP utilizes smart contracts which are programmable codes on the blockchain. These contracts undergo security audits to ensure they have no vulnerabilities to attacks or errors.
Yes, you can use a mobile application or web browser.
Right now you can only pay with the ICP currency. The project is in a strong development phase so soon there will be the possibility of swap with other currencies.