Is it possible to integrate Mattermost in existing web application?

I have few more queries for Mattermost integration
1. Is it possible to have global search of the header as well as content of discussion even though the person who is searching it is not part of any channels ?
2. How to remove member from specific channel ?
3. How to merge two channels if both the channels are discussing about same thing ?
4. How to search via Last feed ? Means the what is last feed for particular channel how to get it ?
5. What is the Maximum file size that can be attached ?
6. What is Database used to store ? If its MYSQL is there any service exposed to get the records ?
7. If I want to change some functionality will it be possible ?