I have found a few dozens of ants in my luggage after arriving back from holiday. Am I at the risk that they will form a colony in my home? Are those ants able to form colonies that are normally gathering food? Will any other kinds of ants be present in the luggage? What will happen to these ants after they start exploring my flat (which is distant from their original colony)?
An ant colony is started by a queen ant (reference). Worker ants are sterile, and cannot start a new colony (reference). The ants in your luggage are worker ants (unless you have a colony in there :) ). The original queen ant never leaves her colony, but during a nuptial flight, new queen ants will land in (hopefully) good nesting sites. (reference) These ants can be told by their wings, which are non-existent in worker ants.
The worker ants have an average life span of 45-60 days (reference), so the ants in your luggage won't be around for very long.