RE #1 - I am a little confused here. Both KMS and KMS GO [which I assume is what you meant when you wrote KMC GO] are proprietary software and are not free nor open. They cannot be used with CE. Please see my explanation here: https://forum.kaltura.org/t/feature-matrix/7057/4
RE #2 - you can set the number of KMC users per partner by going to Admin Console->Publishers->Your partner->Configure->Included Usage->Number of administrative (KMC) users. The default is 10.
At present time, KMC does not support LDAP as means of authentication. KMS does.
KMC and KMS are not the same thing: KMC [Kaltura Management Console] is FOSS [licensed as AGPLv3] and is shipped with CE, KMS [Kaltura MediaSpace], as previously mentioned, is proprietary software and is neither open nor free.
As for access control, you can leverage the content entitlement mechanism for that. As a starting point, please see:
As noted in these docs, this is also how KMS accomplishes the task.
We also support other access control mechanisms that allow black and white listing based on geo location, specific IPs and so on, if that's of interest to you, please see:
RE #3 - multi-tenancy is a very broad term:) In general, the answer is yes, it does. One Kaltura Server can have multiple partners, each partner can have multiple users, with different privileges. Also, as explained in the docs discussing content entitlement, different users can have different privileges on different categories.
The Kaltura API is RESTful, stateless, API. In order to initiate a session [KS], one must provide the partner ID, secret [or the email ID for a given user and a passwd] and optionally a userId.
It is important to note that all web interfaces [Admin Console, KMC, KMS, etc] built on top of the Kaltura Server rely on the API to perform their operations and so, whatever can be done via any of these, can be done from external apps, using the same set of APIs.
For API documentation and code samples, see https://developer.kaltura.com.
A general intro into our API can be found here: https://blog.kaltura.com/api-inside-out-kaltura-architecture/
I hope this answers your questions, let me know should you need more info,