Sounds like a fun project!
Some thoughts:
- Limits
A) regardless of the protocol you use, smartthings has a limit now of 300 devices per location. They also limit you to 20 rooms. They don’t advertise that, but you will start getting error messages if you try adding more than that. So that’s just something to be aware of.
B) Z wave has a hard limit of 232 devices including the Hub up through series 500, which is what the current hub is. Once we get to the newest generation, Series 700, they are going to increase the number of devices you can have, but there’s no smartthings compatible hub that supports that yet.
C) Zigbee can handle thousands of individual devices, one reason it has been popular with lightbulb manufacturers, so you’re going to hit the smartthings limit before you get close to a problem with those. However, the way Zigbee mesh is built depends on devices that can repeat, and each repeating device can typically only accept five children, although it does vary anywhere from 0 to 11 or so. In practical terms, this often means you need more repeating Devices for zigbee then you do for Z wave.
Also, zigbee and Wi-Fi operate on the same frequency, and very strong Wi-Fi can often drown out the very low power zigbee devices used for home automation. There are several threads in the forum discussing what you can do as far as selecting channels and stuff but just be aware that with a setup like yours this might be an issue.
d) As you noted, a typical residential Wi-Fi router normally can only handle about 50 devices, but it sounds like your set up has that covered with commercial grade installation. So again, you would probably hit the smartthings limits first.
E) One other thing to be aware of is that if you do use any third-party bridges, such as the hue bridge, those tend to have their own limits, most commonly somewhere around 50 to 60 devices per bridge. In some set ups so you can have multiple bridges to address this, but smartthings has sometimes had trouble with this in the past so it’s something you want to look into before making any final decisions.
- Wall controllers.
A) if the bulbs are smart, then, yes to get the most out of them you also need a smart wall switch or some kind of panel controller. Obviously this adds to the cost.
In the US, safety codes allow you to have fully automated residential lighting systems in most jurisdictions, with the exceptions that many require you to have a switch control for the attic light for safety reasons.
There are a lot of different ways to set up a smart switch to control the smart bulb, but you do need to think about what’s going to work if your hub is not working. Or if your hub is working but the smartthings cloud is out.
Speaking just for myself, I’m totally comfortable having the accessory switch on a three-way be a virtual three way that requires the hub to be operational except for switches at the top and bottom of a stairway, when I want to be sure they will always work.
When you have a smart switch and a smart bulb, it’s very similar to a virtual three-way where two switches control the same bulb. You need to make the decision upfront about how you will plan for outages. You could end up with a situation where you have no way to turn the bulbs on or off just because there’s an Internet outage, and you have to decide whether that’s OK. Maybe it’s all right for something like a home theater room, but again, it’s not good for stairways or even kitchens or bedrooms. But again that’s a personal choice, you just need to think about it before you start.
B) you also need to decide whether you want the wall control to just be on/off/dim or you also want color controls. You can do some nice color controls with a small tablet on the wall, but you just need to think about what happens again if the Internet is out or the Wi-Fi is out.
Heltun, Sunricher, and RGBGenie all make some very nice Zigbee or zwave wall switches with color controls, but they all require custom code, and I’m not 100% sure that they are working with the new V3 app. Also, what happens at the end of this year when the platform changes? We just don’t know yet what custom options are going to be available for hub connected devices. So that would tend to make me lean towards Wi-Fi control Switches for color controls, but then that opens up all of the other Wi-Fi questions. I’m not the best person to comment on this particular issue, though, because I’m not heavily into color controls. I find the device is themselves appealing from an engineering standpoint, but I don’t have any in my own house. Of course my own physical limitations mean I probably couldn’t use them anyway, so… Hopefully other people who are heavily invested in color will chime in on this issue.
On the other hand, a lot of people are perfectly happy just having some multi button scene controllers for the most popular scenes in each room.
Right now the only one I feel 100% confident will have a manufacturer provided DTH once we get to the new platform is the one from Zooz.
But there are some other options as well.
- Special effects
A) Smartthings has never done much in supporting special effect lighting. They don’t even have good lighting groups. Or simple ways to blink, or color loop, or copy a scene.
So I do know a lot of people who use third-party apps to manage lighting effects if they are seriously into color lighting.
The simplest apps with the snazziest effects available are available for devices connected to a hue bridge. There are at least seven or eight really good apps depending on your particular interests. And there are hue lighting devices in all sorts of formats: enclosed fixtures, individual bulbs, LED strips, sound bars…indoor and outdoor. But device by device they are definitely on the expensive side. Some of the less expensive third-party devices that connect to a huge bridge will also work well with the special effects apps, some won’t, you just have to do some research on that.
Well, those are some of my initial thoughts, I’m sure other people will have a lot more to add. 
