Question about 1675- possible first vintage purchase

[jrlmsla]

Good evening all,
I’ve been a lurker here for a long time. Never had anything of value to say and not a Rolex owner… yet.
I own a few dozen watches Squale, Seiko, Laco, Sinn and micro brands. But I’ve been er owned a “luxury” or higher dollar timepiece. Mostly because I could never decide on which one. As if one would be enough.
Nevertheless here I am again. This time with a question. Basically how do you determine what is or isn’t something that is ok. I’m not worried about real vs. fake.
I was offered a 1675 at what seems to be a good deal. Seems to be because I don’t know really what to look for. After doing some homework and looking through the forum here is what I think it is:
Serial number puts it at 1964
Case is worn/polished with no sharp beveled edges.
Dial is a type 1 I think. Long E. But maybe service dial, although I didn’t see any examples of a long E service dial.
Large GMT hand but that fits serial number.
Bezel is age correct.
Bezel insert—— I think this is aftermarket. Which is the red flag
How much does that affect the value of a watch?
Is there anything else I’m missing?
On to the pics: