Wow, big project! Should be fun.
Deals thread here. Lots of good stuff, members post all the time.
As far as the GE switches, search the forums: statistically, once they are out of warranty, they appear to have a somewhat higher failure rate than a number of the more expensive brands. ( nothing to do with SmartThings, you’ll find the same comments on forums for other controllers.) But then they’re very inexpensive. So a lot of people feel it’s worth it to replace a couple of switches if needed to two to three years in, they still save money on the overall project.
I agree with everyone else who said don’t buy all the stuff at once. Do a room first, and see how it goes for a month or two. After that you can look for bundle deals or volume discounts.
Also I agree with the comments on outdoor motion sensors. 