Is this the final version?
No, we've got a huge list of things to work on for the foreseeable future - keeping your feedback in mind of course.
What are your current priorities?
Performance, improving the graphics and sound, finishing UI implementation and various quality of life features.
Will Preview overlay versions continue working?
Yes, for the time being, however it's not public and will not see further updates.
What can I do to improve performance?
If you are GPU capped minimise AoE2DE to free up GPU resources, you can do this by pressing Alt + Enter and then minimising the AoE2DE window.