I have three questions about the text below.

1. In the context of the text below, can I use "join" instead of "participate"?
2. Can I use "Not so often" instead of "Not very often"?
3. Which is more commonly used in everyday conversation, "Not very often" or "Not so often"?

※Text
Ken: Last week, there was a corporate golf event. I participated and played golf.
Tom: Sounds good! Do you often play golf?
Ken: Not very often. I don’t get many chances to play.

Thank you!

Question

I have three questions about the text below.

1. In the context of the text below, can I use "join" instead of "participate"?
2. Can I use "Not so often" instead of "Not very often"?
3. Which is more commonly used in everyday conversation, "Not very often" or "Not so often"?

※Text
Ken: Last week, there was a corporate golf event. I participated and played golf.
Tom: Sounds good! Do you often play golf?
Ken: Not very often. I don’t get many chances to play.

Thank you!

Answer

1. We usually use "join" with a noun, so you could say "I joined the event" OR we use the phrasal verb "join in", so you could say "I joined in and played golf." 
OR we can say "I took part and played golf." OR "I took part in the event and played golf."

Two other things: saying "and played golf" is bit redundant as it's a golf event, and in my opinion "participated" is too formal and sounds unnatural, and I think it would be enough to simply say "I took part."

2. Yes, you could say "No so often."

3. I think "Not very often." is more common