exhaust fan for bathroom question

MLMIB

my house is in Maryland, built 1959. I have a small master bathroom and a similar sized bathroom behind it. I'm going to steal from the second one to make the master a bit more.... master-ish

problems are...

1) being an old house, an old brick house, there are no vents at all. I know I need to add a vent to each but I'm getting hung up on what I think code says about requiring a vent in an enclosed room for the toilet. I don't know how much moisture a #1 or #2 causes. If I stop the wall 1 foot from the top so it's still connected via that gap to the main room is that kosher? any other thoughts? do I need to even worry about the vent in the separate toilet room?

2) it seems that most exhaust fans want to use the round venting duct but as I have a finished floor above the area in question this isn't an option for me. Is using standard duct work a good or bad idea? experience?

thanks for the help!

Yoyizit

Eight Air Changes per Hour [ACH] are recommended for bathrooms so an 8' x 10' by 8' high bathroom, 640 cu. ft., would need 8x640/60 = 85 CFM, however you can get there.