First, welcome to the community. I must admit, I don't fully understand your situation.
1. You are using a RCBD, what are the factors you are manipulating within block? How do you propose to handle the block effect? Fixed or random effect?
2. What do you mean by "sampling size and methodology"?
3. It appears you are confounding Pen with the block. I could also argue your situation is more aligned with sampling vs. DOE. You could have multiple layers nested depending on hypotheses to identify sources of variation in the study.
4. I'm not sure how simulation would help as I'm not sure how variance is being estimated.
What is needed is to know: What questions you are trying to answer? What hypotheses do you have? What are you measuring? How adequate is the measurement system? How representative is your study of the true population?
"All models are wrong, some are useful" G.E.P. Box