Need help interpreting AncestryDNA results while searching for my biological father

I’m trying to identify my biological father.   I grew up with a dad but had an inkling when I was growing up that he wasn’t my bio dad and I received a message when I was a late teen from a guy claiming to be bio dad. He stated my mom messaged him once I turned 18 or so. I was never told anything growing up and still to do this day have never been told anything. I do not think this guy is my dad and my mom was wrong. 
Here’s what I know:

My closest unknown DNA match
My closest unknown match shares 825 cM with me. Ancestry estimates the relationship as something like half aunt/half great-aunt.
I contacted her, and she told me:
She was raised without her biological father.
She knows who her biological father is.
Her biological father had one son who is her half brother.
There are no other known sons.
I also found that:
One of our shared matches (sharing 63 cM with me) has her biological father’s surname.
The son has several mutual Facebook friends with people from my hometown, even though he currently lives about 3 hours away.
Ancestry parental assignment
I recently started a free trial.
My known maternal half aunt (917 cM) is assigned to Parent 2.
Surprisingly, the 825 cM match is also assigned to Parent 2.
However:
My maternal half aunt and the 825 cM match do not appear in each other’s shared matches.
None of the 825 cM match’s shared matches overlap with any of my known maternal relatives.
Because of that, I’m wondering if Ancestry may have assigned the 825 cM match to the wrong parent.
Another unknown match
I also have a 193 cM match (estimated as a 2nd cousin/1st cousin twice removed).
Interestingly:
He personally knew the man I was received a fb message from stating my mom told him he was my dad.
He told me they were friends, not relatives.
None of his shared matches overlap with my known maternal relatives.
None of his shared matches overlap with the 825 cM match either.
My questions
Does the 825 cM match being assigned to the same parent as my maternal relatives outweigh the fact that there are no shared matches with my maternal family?
Does the 825 cM match and the 63 cM surname match make the 1977-born half brother a reasonable candidate for my biological father?
How would you interpret two separate unknown DNA clusters (825 cM and 193 cM) that don’t overlap with my maternal side—or with each other?
If you were in my position, would you reach out to the man now, or would you keep gathering evidence first?

I’d really appreciate any insight from people who’ve worked unknown parent cases or are experienced with interpreting AncestryDNA results. I’m trying to be careful not to jump to conclusions, but I also don’t want to overlook what may be a very strong lead.