Is "Sokat beszélünk" no good in this case?
Yes, it is good. "Beszélünk" is general talking, "beszélgetünk" is having a conversation. The English sentence could mean either.
Does word order matter here, for instance Mi beszélgetünk sokat?
me too asks this question:
mi beszelgetunk sokat - is that alright?
I think it is correct also. Did you reported this?
I'm afraid, that your sentences are incorrect. The word order DOES MATTER!
what is the difference between sok and sokat
Just the ending, which changes depending on the word it modifies... I believe the "at" here is used to signify an accusative (direct object) ending