I don't know what you mean by "regarding look and free", it's not a phrase that makes sense.
For APIs though, you should use Confluence's REST APIs. These are fully available on Cloud. See https://developer.atlassian.com/confdev/confluence-rest-api
Ah, well, there's layers to that. But you are quite limited on Cloud. From memory, I think you've got two "themes" you can use (chose the default in global settings, and then you can set each Space individually) and you can play with the colour schemes. I suspect the best you can do is messing with the CSS - https://confluence.atlassian.com/display/DOC/Styling+Confluence+with+CSS but I don't think that will let you rearrange pages, just modify the styling.
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