Hello Victor123,
Please find my answers to your questions below.
How many do you need for Production? You need a Cert for all items listed below.
SQL Server SSL certificate
Service Fabric Server certificate
Service Fabric Client certificate
Encipherment Certificate
AOS SSL Certificate
Session Authentication certificate
Data Encryption certificate
Data Signing certificate
Financial Reporting client certificate
Reporting certificate
On-Premise local agent certificate
RDS Server
Can you use 1 certificate for multiple purposes? It depends on which cert. for example, You can use your domain wildcard cert, if you have one, for your Service Fabric Server certificate by adding it as a SAN. That's The root domain must match.
Is "Wildcard" certificate required for Service Fabric? No, but one can be used.
What is the best approach for Test environment? Normally, in the test environments Self Signed certs are used to save money.
Can some Production certificates be reused? It depends, If you want to use a wild card cert and you have added the test server as a SAN on the wild card cert, then it can be reused for that purpose.
How about deployment on local domain? I have heard that CA can't issue a certificate to a not publicly registered address.
This is correct, if the domain name doesn't belong to you, you will not be able to acquire a CA cert. However, you will be able to create self signed certs if it is a test environment.
I hope this helps!