Should be good to go for ETH transactions, albeit dodgy code, let me know what you think.
I was able to send the exact amount of ETH and leave an account to 0, I tested and didn't break sending tokens so far.
I want to add the gas field in the RPC also for Tokens transfer, so that we avoid weird answers from the node. I'll do this once you have a first look at this code.

For future reference, if anyone is reading this PR:
An alternative, cleaner but more complicated solution would be to put gas as a derived form value, using https://github.com/final-form/final-form-calculate, for a future PR.

Let me know what you think about that, I could use final-form-calculate, it works as expected for ETH and tokens, but I can't get rid of a warning message: Warning: Form decorators should not change from one render to the next as new values will be ignored

Thanks a lot, I addressed the comments and it should look better now. No more error, token transfer also have gas in postTransaction now.

Thanks again, comments addressed :)

No problem, I think it makes a lot of sense and simplifies things quite a bit. I've tested, as always, and it looks like it works :)

👍