I'm confused... if you applied inland, you HAVE to stay INSIDE Canada. If both of you aren't living together in Canada then you are Outland.
I'd assume that they've at least accepted your application into processing since it has been at least 4 months, otherwise your application would have been sent back by now. So I would say that the letter they sent was indeed Acknowledgement of Receipt (AOR)
You need to consult with your lawyer to find out more information on it though, since they are the only ones who will have access to it.
In regards to the visitor visa, it is best to wait until your PR process is done and over with so you won't have to bother with it. Most people that apply to visit while waiting for PR are denied anyway.
Then again, there is no harm in trying.
Not everyone needs to do an interview, and if one is requested it would be in the Principal Applicant's home country, not in Canada.
Since you have a lawyer handling your case, they'll be the ones updating you on what steps you need to do next.