Here's our run through on brewing sencha in a kyusu, with a brief guided tasting of Matsuba, our sencha of choice for this video.
Sencha Brewing Parameters:
3-4g of tea per 100mL (~3.4oz)
70-80°C (158-176°F)
1st Infusion: 60s
2nd Infusion: 0s* (as short as possible)
3rd Infusion: 45s
I strongly recommend weighing your tea instead of using a spoon to measure, at least until you're experienced at eyeballing different tea amounts, but generally speaking, one heaping teaspoon of sencha is roughly 4-5g