I have an ARM template that creates Redis resources, basic tier. Usually, Redis spins up fine, but, occasionally, it completes with Azure Redis giving a status of "Failed". All calls will then result in an error. I then have to delete the resource and try again.

This is something that Azure should be doing on its own. When Azure reports that it created a resource for me, there should actually be a working resource there.

The information in this page (https://azure.microsoft.com/en-us/pricing/details/cache/) seems to be wrong - headers for 2nd and 3rd columns seem swapped as they list that Standard is the top performance tier, whereas Premium is in-between Basic and Standard.
Also, you should consider a more effective way to report this type of bugs, directly in the page, rather than going to a general feedback forum which may not be the proper place...

redis cache deployments from the portal always using the same name "redis.cache" and new deployments will replace the old deployment history. Please work on adding a time stamp in the deployment name.

Solution won't recognize .AddUserSecret until you add a nuget package fot it Microsoft.Extensions.Configuration.AddUserSecrets

Is there a way to increase the number of databases? Based on the tier, I am limited to fixed number of databases, but is there a negative impact if I wanted to increase beyond this number? Since the memory of the cache applies across all databases, why is there these limits?

Connecting from java client to Azure Redis SSL port requires us to import the Redis certificate to java kestore. This is not documented in the Redis SSL java client. Is it posssible to add the certificate to JDK itself ?