I’m set to install a Lutron Caseta switch and am not 100% sure of the wiring. Here’s a photo of the box & dumb switches. The left one is getting replaced right now. Ground is obvious. I am thinking the bundle of white in the red wire nut is the neutral. Then they nicely made both load and hot black in the house. I am guessing the top (left) is hot and bottom (right) is load. I have a multimeter, but am not sure what I ma looking for to verify. Any pointers would be appreciated.
use the meter on one wire at a time to see which black wire goes on and off when you flip the switch.
The one that stays on regardless of the switch is the Hot. It’s usually the one on the bottom.
The hot side of load (and line) is typically black so what you’re seeing is very standard. Switch opens the hot path so both wires on a single pole switch are normally black.
The bundle of white wires is the neutrals.
If you’re going to do more of these, invest a few bucks in a non-contact tester. I find it much safer to wave the plastic tip of a non-contact tester over the terminals than to stick multimeter probes in amongst live 120v wires.
Turn your breaker back on and check which terminal always has voltage regardless of switch position.
Thanks. Yep, I think I need to invest in a non-contact tester. This is switch #2 and I have lots (and lots, and lots) more planned. Once I get this one figured out, the rest ought to be simpler. I was happy to see at least enough wires to indicate both ground and neutral are in the house wiring (built in 1972).
FYI, the first was their dimmer from the starter kit & needed no neutral.
Wait until you get to your first 3-way!
In a newer home or with newer switches, you’d find a bare ground wire attached to the switch. And if you had metal boxes, I believe the box would be grounded.
There’s always a neutral somewhere, the question is where.
In many older houses you will find that some switch boxes have a neutral and others don’t. This is true of my own house, which was built in 1955. I could make a guess as to why the ones that have it have it, but it’s not that important: it’s just important to know that some do and some don’t. Particularly before you start ordering switches. 
Good point. Current has to get back to the breaker.
@HalD: LOL! I have a 3-way on the stairs/upstairs hall that is high on my list to replace. Dimmer at the top & normal switch at the bottom. We discovered the issues with two dimmers while re-doing lighting there (no, I don’t like strobes on the stairs). My plan is a full dimmer switch at the bottom, and a Pico remote at the top.
All the boxes in the house are plastic. I suspect that is a plus. Also, so far every box I’ve opened up since I’ve been paying attention has that bundle of white wires crammed in the back.
This stupid little project is taking longer than it should. Too much other stuff going on to let me concentrate on it. I did manage to go grab a no-contact tester and it looks like the top wire is indeed the hot (always gets a tone & red indicator). So I know what wire is what. Now to deal with the long-delayed game of “what does this breaker turn off?” 
I have a good guess though. I hope to wrap this one up tonight, then move on to the fan switch as well.
In general, I love the Zooz ZEN27 for doing 3-ways since it’s only necessary to replace the switch with line.
I do have two spots where I’d like to be able to dim from either side. For those I’m planning to use Leviton dimmers with their matching remotes. Only the main dimmer really dims, the remote talks via the switch-to-switch wiring so both sides effectively work as dimmers to the controlled lights.
Success! Had the evening largely to myself, so I was able to wrap up a few small house projects. Got the switch installed and it works. I’ve set up an automation to turn on the porch light a bit before sundown, so no more coming home to a dark front door. I will see how well that works tonight.
Next up is to figure out how to get that fan switch to integrate. I only found all the threads about how it doesn’t work directly with ST AFTER installing it. 
I have seen mention of an IFTTT workaround, just need to explore that. At the very least, it is recognized in Google Home and I have it added to the Good Night routine there, so have a way of relieving that pain point (teen leaving the darn fan on all night).
Regarding the 3-way, I’ve jumped in one Lutron so will stick with them. Looking at the instructions, wiring isn’t hard, and the Pico remotes are relatively inexpensive. So, I am happy with that solution. It also makes adding more 3(or more)-way setups really easy; just get a bigger face plate and screw the thing to the wall next to the existing box. I have a few new lights in the renovated kitchen that will get that treatment. Bumping a 2-gang box up to a 4- or 5-gang.
Pico Remotes are fantastic! Wireless 3-way switches are so much simpler than trying to figure out 3-way/traveler wiring designs. And the 10 year battery life of the Picos is great. If you’re using a Lutron Smart Bridge Pro, there is even a way to get the Pico remotes to show up within SmartThings as button controllers, although I believe you’ll need a Raspberry Pi running a NodeJS server to do so. Perhaps this is another option to get the Caseta Fan Controller intgerated with ST?