Combining Characters in a Historical -- help!

[ShariMacD]

I'm working on a revision of my screenplay based on historical events from the 19th century. I realize I likely have too many secondary characters. So, a couple of questions:

a) how many secondary characters are generally acceptable (before it becomes too many to keep track of), and...

b) what's the rule of thumb (or is there one) for combining characters when the story itself is based on historical events? That is, when is it okay to bend fact (this particular character was in this particular place, at this particular time) to suit the story's purposes -- or is it always? A scholar who studies "X" (my subject) might not enjoy seeing several historical figures blended into one combined character. But would anybody else notice or care? Perhaps not. So, is it a case of, "This is a film, not fact/reality. The lines are expected to blur. No biggie"? In case it matters, I'm not talking about adding new material I simply made up. It's just a matter of merging 2-3 characters, so the audience doesn't have so many of them to remember.

Thank you!

[Allniter]

NATHAN PAUL JONES
My only regret is that we have not yet begun to fight!