Your right, some folks recommend fans capable of 8 air exchanges per hour, and when the homeowner comes back and says they still have problems with excess humidity those same self appointed experts will tell you to get a bigger fan....BALONEY!!!!! What most homeowners can not get in their heads is that nature abhors a vacuum. I don't care if you have a jet engine for an exhaust fan, the fan can only push out an amount of air equal to what is entering the room. In most residential bathrooms all they have is a higher gap at the bottom of the door to allow air to enter. In fact, in most bathrooms you can actually stand in the bathroom and listen to the fan, then open the door and listen to it, and you will instantly hear the difference in how the fan is working. Four air exchanges per hour is more than adequate if the fan is working at normal efficiency, which means you must have a duct or other means to allow air to enter the room and the ducting from the fan must be correctly sized and installed, however if you don't have a means for air to enter the room, and if your ducting is the typical small diameter flex duct just tossed willy nilly across the attic your fan does not run at peak efficiency. In all likelihood it is not even running at minimal efficiency. When we design the fans system for institutional shower rooms such as those in a high school locker room with upwards of 36 showers all working at once, we only design for 4 exchanges per hour, but you can sure bet that we design rigid ducting that is properly sized for not only the cfm of the fan, but compensating for the length of the run and we install dedicated return air ducts that will allow and equal or greater amount of air to enter the room.

In a steam shower, when you're done "steaming" all you do is turn the main shower on and the spray of cool water will almost instantly cause the air temp in the shower to drop enough to cause the steam to condense, it clears the air almost immediately. It can be advantageous to have a vent inside most any shower. But you just don't want the duct work accessible to steam when using the steam function, thus the desire for a positive closing damper. You could go with a single fantech fan with a couple of vent grills, one with a positive damper in the steam shower itself, the other outside the shower in the main area of the bath. Only turn on the fan when using the shower as a regular shower, or only when done using the steam shower. In a typical small bath you can run a fan with about 1.1 CFM per sqft of floor space. In larger baths you can size it off of fixtures; 50cfm per "typical" fixture and 100cfm for things that generate more moisture like jetted tubs, steam showers, etc. When you start getting towards the 200cfm fans, it's best to install more than one vent grill in the ceiling. Pulling that much volume through a single grille can result in turbulent air noise. If you have a long/twisting duct then more CFMs might be needed due to static losses in the duct. Your builder would be able to help you with that though. Spring-loaded and gasketed dampers are about $30-$50 depending on size.

Hi abwhitney: In lieu of an expensive frameless shower door, many people on this forum have opted for a shower curtain instead. You can get a curved shower curtain rod or a straight one and then a liner and the actual shower curtain. There are a lot of nice shower curtains with large grommets that will give a modern look and are machine washable. I saw a nice, clean white shower curtain with the big grommets at Lowes this weekend. In terms of a bathtub, I think Kohler has quite a few to choose from. If you have the room, I suggest you look at the Kohler expanse tub. It's acrylic and easy to clean. I agree with pricklypearcactus in that large ceramic 10 x 13 or porcelain tiles will be easier to clean and much more low maintenance than marble or natural stone. Many tile manufacturers make ceramic and porcelain tile that mimic the natural stones quite nicely. For ventilation purposes, many on this forum recommend the Panasonic Whisper vent fan. I'm not where the intersection of modern versus contemporary lies for you, but Duravit and IKEA make wonderful vanities for space constrained areas. Take a look at the IKEA Godmorgan vanity and medicine cabinet. Good luck! Here is a link that might be useful: Kohler Expanse Tub

I don't know about any shower pans but the Kohler cast iron pan I will be installing. I have one that is 36x60". It has a center drain. There is a 30"x60" that has the drain at either end, to be used where a tub had been. It also comes in a 36"x48" I think. About the other questions regarding a glass screen, I can't tell you.