Being proud of 100% test coverage is like being proud of reading every word in the newspaper. Some are more important than others.
Alternative to estimates: do the most important thing until either it ships or it is no longer the most important thing
pair programming is not a "go faster" strategy, it is a "waste less" strategy (which often results in going faster)
"Do it right and you won't have to do it over". Yeah, until "right" changes. And it always changes.
If you know how to design the software, design the software. Otherwise implement now, learn, and design later.