There is theoretical limit of 146 certificates to be added per Virtual Service.
This is because the configuration entry holding the names of the certificates has a maximum length of 1023 characters.
If we assume that the certificate names (Certificate Identifier) are two characters long, plus the .pem file extension and the mandatory spaces between the names, this gives 146:
Certificate Identifier (2) + .pem (4) + <space> (1) = 7 characters:
1023/7= 146 total certificates with a 2 character Certificate Identifier
If you are using longer certificate names, this limit will be lower.