As far as the size of your house… Smartthings supports both Z wave and Zigbee protocol. Both are mesh and work by having one device pass a message along to another device which then passes it along until it gets to the hub. This can work very well and helps improve the battery life of individual devices by keeping the power requirements for each individual device low.
However, only mains-powered devices can act as repeaters. Battery powered devices do not.
If you’re using some plug-in Z wave motion sensors, that can help, because they will also act as repeaters. But almost all of your other sensors will not be repeaters.
So in a house as large as yours, you may need to buy some additional devices just to act as repeaters. The easiest are what we call in the forum “pocket sockets” which are plug-ins that you can then plug a lamp or a coffee maker or whatever into. There are some that are pretty inexpensive, around $25, and obviously they’re easy to move around to wherever you need them.
It’s just something to be aware of as it can affect both device selection and budget.