This would be covering a shower and a whirlpool tub, but not directly above either. Also, thoughts on it being equipped with a heater (in Houston)? Are there other details you'd need to know to help make this decision?

I would look at Broan or Panasonic and get one that is humidity-controlling. It will come on automatically if the humidity is too high.

I have this one and really like it. 3 different cfm settings to choose from.

Paired with a timer switch. Hit 15 or 30 minutes when we start the shower. I read that the humidity sensors could run the majority of the day in Houston.
Panasonic FV-05-11VKS1 Whisper Green Select Fan https://www.amazon.com/dp/B00JALSA0C/ref=cm_sw_r_cp_api_i_3HVdDbHFB1MWE

Do you just set the cfm on install and leave it?

I'm not clear....is this a new install or are you swapping an old one out?

If you're swapping an old one out you need to consider inside install vs. attic install options.

Our master bathroom has a water closet that has a toilet and a dedicated exhaust fan, but we want to add one to the main bathroom area to exhaust the steam from the shower and bath. Currently renovating the bathroom and have access via the attic.

Room is about 120 sq ft with 11 ft vaulted ceilings.

Wow ! How do you get in a room 11 INCHES High!

Assume you mean 11 ft which calculates to needing 175 CFM fan.

I use Panasonic almost exclusively. They have several options but my go to is this recessed light/ fan. I usually have the fan on a digital timer vs humidistat, but have used humidistat a in the past. Timers are easy to touch when needed and to me less problematic. This one moves a good amount of air and keeps the steam down. And I like that it blends with the other recessed lighting in the room.

https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/ventilation-fans/whisperrecessed-ledtm

I've also used this fan when people want a heat option. The exhaust works well and it puts out a lot of heat. It's more noticeable in the room obviously. This one has a cfl light, there's also one without a light. The heater requires a dedicated circuit. Both customers have been happy with theirs.

https://na.panasonic.com/us/home-and-building-solutions/ventilation-indoor-air-quality/ventilation-fans/whisperwarmtm-lite

I also did a Panasonic whisper quiet.

I'd go bigger than 80-110CFM. They make some that are 150, 290 even.

There is a switch that is accessible from inside the grill. Just pop off the grill and change the switch.

It all depends on the size of the room.

We have a 6' x10' and I'd say the 110cfm is about as low as I'd go. I tried 50cfm and the top of the mirror will start to fog up. 80cfm does better, but 110cfm almost guarantees the mirror stays clear.

I figure 10x11 should be looking at 150cfm+. Keep in mind noise is much reduced in either case by going 6" exhaust. I did 4" for 110cfm and should have just gone ahead with 6".

At Stearns Design Build we typically install the Panasonic Whispergree with a humidistat so that the fan comes on and goes off based on need. When sizing the fan keep in mind that you are pulling conditioned air out of the house, which, in most circumstances will be replaced by unconditioned air. Another important issue is how and where the humid air is vented to. All too often we see it vented into the attic. This is never good.

I vented straight outside through roof.

Funny thing: in that small project I cut a 4" hole in the roof during summer and felt a strong exhaust of hot hot air through the hole.

I've since installed a ERV4 1000cfm attic fan to remove hot air. We have three gable vents, but no soffits. Seems to be working... 130-135F down to 112-120F.

Venting air out of your attic can cause air to be pulled out of the house. A good way to reduce this is to foam seal all of your plumbing and electrical penetrations into your attic. Plumbing penetrations are easy to find because you will see the vent stacks. If you have supply lines running through the attic there will be additional plumbing penetrations but in the same area for the most part. Electrical penetrations are more difficult to find. There will frequently be a penetration above switches. Any ceiling light or receptacle is also a place where conditioned air can easily be pulled into a hot attic. Also, seal the edges of ceiling registers. If you are foaming at a fireplace or furnace flue, use fire-rated foam. This is the low hanging fruit of an energy retrofit and something that most homeowners can easily do for themselves. At Stearns Design Build we depressurize a house to find leaks before every remodeling project. We let our clients know that these are things that they can easily do themselves to reduce utility bills.