Please find the responses to your queries listed below :
1) How can I remove “Proudly powered by WordPress | Travel Log by WEN Solutions” from the footer? And What Payment Gateways are supported for booking tour packages?
The feature to remove the footer credits links from the free Travel Log theme is not available on the Travel Log theme. You can edit the copyright text in the footer, however, developer credits are mandatory in free WordPress themes.
2. where can I find dummy data for travel log theme and how to import dummy data ?
The dummy contents for the soon available bundled with the theme itself with theme update soon, with import functionality to be handled by theme addon.