Limit Maximum Connections

Hi,

is there a way to set a limit to the number of connections that a single user can have?
I would like to set a different max connection limit for different user groups, I thought that I could use Cb Subs to set an integer field with a number depending on the subscription plan, but then how can I check that users didn't reach the limit and block them from asking or accepting new connections?

Regards,
Gabriele

Ok, I partially resolved creating an integer field (counter) in CB and using auto actions plugin.
Counter increases on subscription or buying specific plans and decreases adding or accepting connections.
When counter reaches zero, on next adding or accepting connection user is redirected to a page where he is invited to buy more credit.

Now I wonder, is there a complete list of substitution that I can use in the Conditional field inside Auto Actions Plugin?
Is there a way to evaluate fields from tables different from jos_comprofiler and jos_user (fields from tables related to other components, for example Aup)?