Maaser

I’m looking for some information on maaser. Such as:

1) When did maaser change from fruits/vegetables to 10% of your money?

2) Where is this halacha written?

3) What do you take maaser off of? Is it your salary after taxes have been removed? Is it after taxes and loans have been paid?

4) Do you have to have your maaser “paid off” by Rosh Hashana or can you build a fund with it?

5) If you are a farmer in Israel today, do you take maaser from your produce AND your cash? That would seem redundant to me.

I’m going to discuss this with my LOR but I figured I would flesh out my questions a bit here, before talking to my Rabbi so I have my questions fully formed. Discussion always brings up new points to ponder!

Thank you for your help!