What is best practise in variable font development?

I am working on my first type family. It has one axis (weight) and for now two masters (thin and black). I draw about 80% of the set (draft quality) and before stepping into the finalization phase I would like to check a few things. 

First is that I draw in 1000upm, I thought it's a standard these days, but a friend told me that 2000upm is maybe a better option for the variable font and that Google Fonts variable projects use 2000upm. What's your opinion? Sounds logical to me, especially because my font has softened corners, and I feel that the 1000upm integer grid sometimes offers two ugly options to choose between. (I also see the kink near the top terminal in the regular instance) 

Secondly, I feel that just thin and bold masters are not enough. Here is the example of the lowercase "a" as it looks currently. While it's not perfect, I generally like the look in thin and black, but when I check interpolation at 400 (Regular) horizontals and lower bowl-to-stem joint are too thin. Is it usual to add intermediate master, or you rather adjust thin and black masters? 

Also, I would highly appreciate any other recommendations besides these two I mentioned.

Thanks!