Devices which are repeaters will pass the messages around but you’re still better off with the hub in the center. Z wave has a maximum of four hops per message into the hub, zigbee home automation profile which smartthings uses allows for 15 into the hub and 15 out. So place the hub centrally and you probably double the coverage. This is all covered in detail in the whole house topics.
There is no official integration with nest. Nest won’t allow it because smart things doesn’t Limit its Control of the devices the way nest wants. There is an unofficial integration, but using it is actually a violation of your terms of service with nest, and they could shut it off someday, you never know. That’s what happened with Chamberlain and myq.
https://support.smartthings.com/hc/en-us/articles/204733384-Does-SmartThings-work-with-Nest-
As far as “A works with B and B works with C,” yes, that’s so, but it doesn’t mean A can issue commands that C will receive or pay attention to. You can’t get to the haiku fans from SmartThings through nest. There are other fan options that do work with SmartThings, so again you just have to do your homework and then decide what you want. Also, “works with” has different meanings in different situations. It doesn’t mean “gives you the same features and control options as the native app.” Some of the stuff that “works with” nest just means that nest will send a message if it’s in home or away mode. So you really need to look into the details of each potential integration.
As far as IFTTT, that’s always an official integration, which is good, but it’s a very limited integration. Again, you have to check each service/channel to see exactly which features are available. For example, some devices will tell IFTTT that they have been turned on, but cannot be turned on through IFTTT. For other devices it’s the reverse.
For example, the nest IFTTT service will tell you when it’s set at home, but it won’t let you set it to home. And it will let you turn on a fan, but only for your single default period.
IFTTT is useful for many things, and I use it myself a lot, but it’s not a substitute for a full two-way integration.
Do not combine smart bulbs with a smart switch that controls the current to the bulbs if you plan to use the switch frequently. The inrush current to the bulb will burn out the radio over time. This is true whether it’s a hue bulb or a Cree smart bulb or A zwave bulb or a LIFX bulb. Smart bulbs are intended to always be on full power and then the bulb will decide for itself how much current to draw. See the user guide for any individual bulb you’re considering using. Again, there are ways around this, they are discussed in detail in the hue switch FAQ. But the short answer if it is if you are using the GE smart switches, you should plan on using dumb bulbs with them. If you want the color changing features of smart bulbs, then check the FAQ.
There are some Devices that allow for each outlet to be controlled, you might want to look into those for a project of your size.
As far as infrared and outdoor cameras, yes, it works very well as long as the infrared is positioned correctly.
The August locks aren’t going to work with SmartThings. If you’re going to use SmartThings as your home automation controller just look at any of the locks that do work with it. You can check the official compatibility list, but both the Yale and Schlage zwave are good locks.
If you’re going to get into DIY home automation like SmartThings , you just need to get in the habit of reading the specs for every model that you are considering. There’s a lot of variation even within a brand. For example, one Switch might work just fine with fluorescents and another might not. If you’re having trouble understanding the spec sheets, just ask in the forum and someone will be glad to help you. If you don’t want to read spec sheets, you might consider homekit instead. There’s a much smaller selection of devices to choose from, but everything works with everything else and it’s all pretty straightforward. You can get an August lock, an ecobee thermostat, Hunter Apache fans, and any of several switches and it’s just a much simpler system to spec out. If there’s a HomeKit logo on the box, it will all work together.
SmartThings is a much more flexible, versatile system, but the cost of that versatility is that you do have to individually verify that each possible device will work in the way that you want it to work with your other devices. It’s a lot more work, both before and after installation. That’s still worth it to many people, but it’s just a decision you have to make for yourself.