Depending on the criteria listed below, you will be able to choose a processor that is right for you.
Number of users
10-15 is suitable for the usual 8-core special lead processor, with a clock frequency of 2.2 GHz, the cache volume is not particularly important, the main thing is to choose a processor according to your budget.
20-100 is already a fairly large number of users and so that they can use the server without difficulty, it is worth choosing a good processor. You should pay attention to a processor with a number of cores from 12 to 16 and a good amount of cache memory so that commands are executed faster.
More than 100 people - this can be compared to a large company, and in such companies it is important that everything works without interruptions and very quickly. In such cases, it is worth taking processors with a number of cores from 24 and a large cache of memory. It is best to use a server with multiple processors at the same time, this will allow it to work more stably and efficiently.
Information processing
The more information you need to process, the more cores your processor should have. This is a little incorrect wording because there is a multithreading clause. For example, you will have enough of an 8-core processor with 8-12 threads and a frequency of 3.2 GHz to process a large amount of information. Thus, it is necessary to take into account multithreading when choosing a processor for the server.