Parallel.ForEach in C# when number of iterations is unknown - c#-4.0

Question

I have TPL (Task Parallel Library) code for executing a loop in parallel in C# in a class library project using .Net 4.0. I am new to TPL in C# and had following questions .
CODE Background:
In the code that appears just after the questions, I am getting all unprocessed batches and then processing each batch one at a time. Each batch can be processed independently since there are no dependencies between batches, but for each batch the sequence of steps is very important when processing it.
My questions are:
Will using Parallel.ForEach be advisable in this scenario where the number of batches and therefore the number of iterations could be very small or very large like 10,000 batches? I am afraid that with too many batches, using parallelism might cause more harm than good in this case.
When using Parallel.ForEach is the sequence of steps in ProcessBatch method guaranteed to execute in the same order as step1, step2, step3 and then step4?
public void ProcessBatches() {
List < Batch > batches = ABC.Data.GetUnprocessesBatches();
Parallel.ForEach(batches, batch = > {
ProcessBatch(batch);
});
}
public void ProcessBatch(Batch batch) {
//step 1
ABC.Data.UpdateHistory(batch);
//step2
ABC.Data.AssignNewRegions(batch);
//step3
UpdateStatus(batch);
//step4
RemoveBatchFromQueue(batch);
}
UPDATE 1:
From the accepted answer, the number of iterations is not an issue even when its large. In fact according to an article at this url: Potential Pitfalls in Data and Task Parallelism, performance improvements with parallelism will likely occur when there are many iterations and for fewer iterations parallel loop is not going to provide any benefits over a sequential/synchronous loop.
So it seems having a large number of iterations in the loop is the best situation for using Parallel.ForEach.
The basic rule of thumb is that parallel loops that have few iterations and fast user delegates are unlikely to speedup much.

Answer 1

Parallel foreach will us the appropriate number of threads for the hardware you are running on. So you don't need to worry about too many batches causing harm
The steps will run in order for each batch. ProcessBatch will get called on different threads for different batches but for each batch the steps will get executed in the order they are defined in that method