Hari Do you support to access my data via API?
Not sure what kind of API are you referring to, but FreeFlarum has simple REST API to list all or specific forums, validate forum name, etc... There's no documentation for that, but it'll be no problem to me to answer any questions that you might have about it, since I developed it. As for Flarum, it has a rich REST API built-in, but that's not related to FreeFlarum
AFAIK Flarum has the Embed extension that allows you to use iFrames with your forum. But that's again not directly related to FreeFlarum, which has no support for embeds (because it doesn't need to, unless you want to frame the main FreeFlarum website)
Hari Do I need to upgrade to any premium plan? How much it would cost?
FreeFlarum is free and will always stay free. We are not a company, nor a commercial entity. There will be no paid plans, but donations are always welcome.
Hari Can we expect 99% uptime?
There are no statistics, but we do our best to ensure that FreeFlarum stays always online.
However I must say that I am slightly concerned about your questions in a way that FreeFlarum might not be ideal for your needs. It is operated in our spare time, and while fixes and updates are published relatively fast, we cannot guarantee that it is at a level that meets your expectations. You asked about questions that are related more to Flarum rather than FreeFlarum (please note that FreeFlarum and Flarum are two completely different platforms unrelated to each other).
I therefore assume that you are looking at us more from a commercial point of view. In my opinion I think that self-hosting your forum might be the best option for you. If you lack the resources to do so, please consider checking out the Blomstra service, which is a paid and professional Flarum hosting provider, operated by @luceos)
