The Hypothesis Test Designer

Help me design a proper test of this business question.

The question/claim: [DESCRIBE — E.G. "DOES THE NEW PROCESS REDUCE
ERRORS?"]
What I can measure: [DESCRIBE THE DATA I CAN GATHER]
The stakes: [WHAT THE DECISION IS]

Provide:
1. The null and alternative hypotheses, stated clearly
2. The right test for this data and question, and why
3. The data and sample size I'd need
4. What significance level makes sense given the stakes (and what a false
   positive vs false negative costs me)
5. How to interpret the possible results

Keep it rigorous but explain each choice so I understand what I'm testing
and why.