Dear Erdoğan Uğuz,
Your 3000 users can access the server via a web service. Technically, there is no restriction on the web service usage. Though, you should keep in mind that you will have to select appropriate (mostly, hardware) characteristics for your server to ensure it works normally under the workload your users apply.
As for the client licenses.
On the one hand, technically, when your clients connect to your server via a web service running thanks to the infobase, it does not consume client licenses. This is what I wrote in the message about. So, a web service is simply a way to access an infobase's data, and this way is not licensed separately.
On the other hand, according to the license agreement, there should be a client license for each client computer from which your users access the infobase. So, you should ensure that you have client licenses for the maximum number of users that simultaneously work with the web service.