Haha yea it's a fair bit of work involved but worth it if you've got a day free 😂

I'm not super familiar with that umami seasoning, and as good as it looks the mushroom version of umami has always been it's own thing in my opinion? Probably because of it's own unique flavours it brings to the party. It could totally work though!

Fish sauce would be a hard no though lmao.

If you happen to have miso paste or powder on hand it could work as a good alternative though, just watch the salt content and reduce the soy as necessary.

Or just go buy a small bag of MSG lol that stuff's cheap.