OK, thanks all.
Still not 100% sure about how much yeast to use.
I'm sure that the tin is exactly the same as the sachets. The sachets have 7g in, which is at least 2 teaspoons, probably more like 2½.
But above someone was only putting in less than 1 teaspoon. I guess that too much is as bad as not enough.
Two teaspoons is the right amount for the ingredients you posted. I'm about to make a similar loaf (using 450g of spelt) and it calls for two teaspoons. You'll be fine with that.