cab crew?

[union pacific 844]

how many do i need for 4-8-4's?

[Desertdweller]

Generally three:  Engineer, fireman, head-end brakeman.

Les

[RAM]

In passenger service you only had the engineer and firemen.

[ebtnut]

That may depend more on what's behind the tender.  If there were a lot of sealed express cars or mail storage cars, the head end brakeman may still ride the cab. 

[union pacific 844]

one with mix freight cars   one with passenger cars

[RAM]

I think a mixed train would have three.   Engineer, fireman, head-end brakeman.

[ebtnut]

You would still typically have a five man crew on a mixed train.  The conductor and rear brakeman would normally ride in the coach/combine.  The headend man might also ride there if the train was typically short.  If enough freight cars were assembled to make a decent train (say 10+ cars), then he would likely ride the cab to be close to the tender for coupling and uncoupling at the head end.