Can I apply for a visa extension in Udon Thani instead of Bangkok, and how will the extension dates work?

Hello -

I entered Thailand under visa exempt and planning to apply for extension. My questions;

1. Can I apply the extension in another province as I spent most of my time here (Udon Thani) or should I go back to Bangkok to extend in MTT?

2. If I extend earlier (my stamp run out on 17 April) will my extension dated from the date I apply or continue from the original stamp date?

3. And the last one, is the IO open on 11-12 April before Songkran?

Thank you in advance