I'm happy to answer your questions, but the first thing you will need to do is change the way you are thinking about your videos. When videos are hosted in SharePoint, they are managed in SharePoint like any other file (Word, PowerPoint, Excel, PDF, etc.).
1. There will be no Stream admin center. All files will be in SharePoint and they will become part of the rest of SharePoint that is managed in the SharePoint Admin Center.
2. You will want to think about who owns the videos and how they share them. Do they share them with the entire organization? Do they share them with individuals? Are they just meeting recordings? Each has a different answer.
If you are sharing them with the entire organization, then they will most likely go into a Communications site in the Documents library. They will then be surfaced using SharePoint web parts on the site's page(s).
If they are shared by a smaller group of users, then you have to ask if that group of users has a team in Microsoft Teams or a SharePoint team site that they already collaborate in or not. You put those files in a team site in both of these situations.
If it is just a meeting recording, it will go into the OneDrive account of the person who owns it and is shared out from there -- just like all meeting recordings from Microsoft Teams have been saved for the past 2 years.
3. If you used the Stream (classic) web part to display videos on your intranet pages - they will only work until February 15, 2024 if you move the files manually or redirects following migration with the Stream migration tool will continue to have working redirects until February 15, 2025. Because the video files are stored just like documents in SharePoint, you will use web parts to display the videos. The most common web parts right now would be the Hero, Highlighted Content, and File Viewer. There is a new Stream (for SharePoint) web part that is in development, but it will not be available until this Fall. Bottom line is that you will need to update all of your links and/or replace the web parts.
A great resource for how to do this is found at https://aka.ms/StreamPortals
4. Any video file that is stored on SharePoint right now does have embed code available for use inside an organization's network. Here is a link to instructions for how to get it from both SharePoint and from OneDrive.https://support.microsoft.com/en-us/office/embedding-stream-content-in-third-party-sites-b50b6cd2-be...