I think the nootropics people claim that most green tea has a little bit too little L-Theanine to get the most out of it biochemically, but I'm not sure.

They first extracted L-Theanine from Japanese gyokuro tea, which is green tea grown in shade and it has a lot of the wonder drug, but it's pretty expensive.

Anyway, green tea is great as it is, so it's up to you!

Possibly not. You can try, it's quite safe. I take it with no caffeine at all because I caffeine stresses me out during deadlines.