The number of tasks is not really that important, the load average numbers (at the top right) tell you the real story. Depending on the kind of resources your server has and what are these tasks actually doing, ~4000 may not be too many, it may even be too little.

Given the screenshot you posted, I cannot tell if load average of ~2.5 is good or not, the rule of thumb is that an efficiently utilized server should have the load average be around 2 X the amount of cores in the server. Less then that usually mean the server is underutilized, and more then that may mean you have a resource bottleneck somewhere.

You can press '1' to get CPU utilization breakdown by core, that will also tell you how many cores you have.