Keine Ursache = You're welcome

I can see that the word “bitte sehr” has a meaning very similar to “bitte schön” of which one is “you are welcome" according to this translator “https://dict.leo.org/”.

1. When is it more appropirate to use “bitte sehr” instead of “bitte schön”?

2. I understand that “bitte” can also be used to express “you are welcome”. When is it considered appropriate just to reply with “bitte”?

I can see that the word “gern gescheden” also has a meaning very similar to “bitte schön” of which one is “you are welcome”.

2. Is it fair to say that “gern gescheden” should be used in more formal situations? whereas “bitte sehr” and “bitte schön” both should be used in more informal situations?

4. Are there some regions in Germany where either “gern gescheden”, “bitte sehr”, “bitte schön” and “bitte” is more common than the other?

Hallo RexV!

Let's have a look at your questions! 

1. Both terms are pretty much interchangeable. “Bitte sehr” might be a little bit more formal and is often used by a waiter or waitress when serving food and drinks, for example.

2. “Bitte” can be used as an abbreviation of “bitte sehr" or “bitte schön”. Usually you can go by what the other person has said, for example:

• Person A: “Danke.”  → Person B: “Bitte.” 
• A: “Danke schön” → B: “Bitte schön.”
• A: “Danke sehr.” → B: “Bitte sehr.” (These examples can also be used the other way around, e.g. A: “Bitte” → B: “Danke.”.)

3. Yes, “gern geschehen” is slightly more formal. You can also think of it as saying “My pleasure.”.

4. All terms are pretty common in all of Germany. Usage can depend on the context, the person you're talking to, but also personal preference. 

Viele Grüße,

Julia

Danke Danke!

Bitte!