What are the visa options for Russian nationals on a METV in Thailand regarding extensions and border runs?

1 - get 60 days on arrival ?

-> Yes.

2 - 1900 thb extension possible ?

-> Yes. But I would check the local policy at the immigration office where to stay to be sure can get it for every entry. (most likely yes, but there are 80+ offices nationwide)

3 - extension for 7 or 30 days ?

-> 30 days.

4 - if make border bounce on the last day of visa, can get 60 more days, which can be extended again (total 240-270 days)?

-> You will be stamped for 60 days on every entry on or before the "valid until" date on your visa sticker. It's eligible for 30 days tourism extension.