As it says...It's recovering. You have to wait.

Refer to below Ed Pollack's article for analyzing your Buffer pool.
https://www.sqlshack.com/author/edward-pollack/

If it works for enterprise edition, it should work for developer edition too. Also, IIRC...there are no limitations with standard edition either(I could be wrong here, been a while working...

Yes, you can uninstall SSMS version 16.5.3. It shouldn't impact your actual SQL Server services(if you have them installed).

RCSI is not a magic switch which can eliminate all kinds of deadlocks. Below are couple of excellent resources which might help understanding pros and cons of enabling this feature.

In a traditional setup yes, there's no need for shared storage for configuring Availability Groups. But we can combine AGs with FCI where AGs can use a failover cluster instance...

Read through AlwaysOn stairway, This should provide answers for all your questions...
http://www.sqlservercentral.com/stairway/112556/

dbatools(Leverages powershell) has fantastic migration solution. FYI
https://dbatools.io/functions/start-dbamigration/

We used to run into this issue in the past and we were using VBS script to fix (https://support.microsoft.com/en-us/help/969052/how-to-restore-the-missing-windows-installer-cache-files-and-resolve-p)
Well, now there's a tool called "FixMissingMSI" from Microsoft to...