C# Multithreading Model

I've a c# single threaded application and currently working on to make it multi-threaded with the use of thread pools. I am stuck in deciding which model would work for my problem.

Here's my current scenario

While(1)
{
    do_sometask();
    wait(time);
}

And this is repeated almost forever. The new scenario has multiple threads which does the above. I could easily implement it by spawning number of threads based on the tasks I have to perform, where all the threads perform some task and wait forever.

The issue here is I may not know the number of tasks, so I can't just blindly spawn 500 threads. I thought about using threadpool, but because almost every thread loops forever and won't ever be freed up for new tasks in the queue, am not sure which other model to use.

I am looking for an idea or solution where I could break the loop in the thread and free it up instead of waiting, but come back and resume the same task after the wait(when the time gets elapsed, using something like a timer/checking timestamp of when the last task is performed).

With this I could use a limited number of threads (like in a thread pool) and serve the tasks which are coming in during the time old threads waits(virtually).

Any help is really appreciated.