Visa extension question

>Because I would like to extend it another 3 months, I know that I can go to the Immigration office in HCMC and pay $10 to do it,

No, first time it will cost you 35 USD

>but don't know how much time they'll give me.  Will they extend it 3 months more?? 

Yes. Depending how much time you ask for, but not more than 3 months.

>Will they extend it as a B3? 

No, it will be a C2

>Will they say anything once they see that it's a business, not tourist visa?

No

>What's the difference between a renewal and extension?

No difference.

>And finally, what other docs besides the passport and N14 form will I need?  Is there a link to this N14 form online?

Read this https://www.expat.com/forum/viewtopic.php?id=46856

Thanks for the info and response.  However, the link for the form brings up a form with too many symbols which I don't think they'll accept.  And I had read that post page the other day, however because it's 2 years old, who knows how reliable it is.  So thought I'd ask.

My response on that thread was June this year.

Anyway, the reason you have those weird symbols is that your PC does not have the Vietnamese fonts installed.

Go to a public PC (internet cafe with a printer) or a Vietnamese friend's PC and download it, chances are that they'll have the fonts installed. Print it out from there.

Let me know if you still have a problem.

Ah, okay.  Thanks!  I use the V-keyboard over on the Control Panel button, but there's another one that can be installed which I haven't done.

Also, that part where you need someone to vouch for you... if I'm staying at a guesthouse, does it have to be the owner?  If I know a Vietnamese person here, could it be them?

Anyone who is willing to vouch for you is OK with the immigration office.
The important thing is to get the local police where the sponsor stays to sign.

That is why many are paying to use agents since the agents sponsor them!!