Specific supported device hardware can be found in the following wiki's:
Officially Supported
https://docs.hubitat.com/index.php?title=List_of_Compatible_Devices
Community Drivers
I use a Schlage myself and haven't missed a lock or unlock once.
MyQ add a contact/tilt sensor and you're good. I don't think their app supplies access to the internal contact sensor or something along those lines.
Life360 for geofencing works, you can also combine presence devices/sensors for redundancy.
Echo speaks
A lot of users here use Sonos fine.
WebCORE
Honeywell Wifi Thermostat I have two and use HubConnect with ST and it works fine with no API limitations that I've found so far. I may change it to local HE hub at some point but right now it isn't giving me any problems.
Samsung TV integrations even on ST are garbage. I have Samsung TV's from all of the last 6 years and they all have little quirks. I left them on ST for now and use HubConnect for these. All of them have the LAN disconnect bug and changing them to wifi helps but if the TV is off for a few days they will drop off too. One of the 2017 model's has a "SmartHub" that the screen connects to and reboot it daily to keep the hub from misbehaving. A couple of the other ones I have to reset occasionally by holding the power button on the remote until it reboots to get it be seen on the network as well as to enable the firmware update option.
Not sure about Yamaha receivers but if you have a DTH for it in SmartThings someone can probably convert it pretty easy.
I have about 150 devices and a single hub. With your setup you should be fine. Some people have multiple hubs because they have separate floors and want best possible signal on each floor, others use it to segregate bad-actor devices (some wifi bulbs come to mind here) so they don't route other devices through them. Sometimes users will find an app they want to use but it consumes a lot of resources for whatever reason and for performance reasons choose to add a hub to split up the workload.
If you run multiple hubs there are several ways to connect them all with their own ways of working but in general try to keep local processing with local devices to that hub and then have global rules that span the devices as needed. Each hub acts as it's own controller.
Most radio frequency interference issues are on the Zigbee side. Just pick a channel that is fairly clear and you should be fine. Usually 20 or 25 is the preferred channel. Avoid 26 it has some limitations.
Keep your ST hub in case you want to do OTA firmware updates in the future for any ST devices.
