There are a number of good books on randomization methods in clinical trials, but I often recommend the book by Vance Berger, who takes a focused look at how even apparently rigorous randomization methods may leave some room for bias: Selection Bias and Covariate Imbalances in Randomized Clinical Trials.
Regarding your specific questions:
I have been tasked with designing an RCT and although I am familiar with the general principles of randomized block designs, I wanted to hunt down a good reference that could take me through the process step-by-step.
1) How do I determine the optimum block size?
This is typically based on a trade-off between study size, number of treatments undergoing comparison, and efficiency. I typically favor either 8-unit blocks or blocks with varying size (e.g. 4-8-16).
2) What are the pros and cons of a large/small block size?
A large block size minimizes guessing and the predictability of the last allocations, whereas a small block ensures less imbalances in enrolment, especially if blocking is enforced per center and not overall.
3) Is there a standardized process for assignment within a block?
Not that I am aware of. I usually refer to statistical packages or dedicated websites such as randomization.com
4) What is the most accepted reference for these questions?
On top of Berger's book, have a look at Randomization in Clinical Trials: Theory and Practice.