The maximum file size limit depends on your plan.
The files stored in SendBird servers are kept temporarily and we haven't decided how long those files will be available. We'll announce it shortly and it will be reasonably long period. ( You don't need to worry about files you're uploading or already uploaded since we won't delete any files without advance notice. )
If you use host files on your own servers, and provide a direct link to these files, then naturally there is no size limit.