Lighting
I can't say enough good things about Volt. My yard is covered in them. Five years in and I haven't changed a bulb yet. Fixtures are gorgeous and rock solid. I expect them to last a lifetime (mine, anyway). Nothing else I've ever tried has come anywhere close. Crazy expensive, worth every penny.
If you want them to come on dusk to dawn, that's fine. Also plan some sort of manual override (like a switch in the house or smart home capability). You'll want to be able to turn them on and off at will. Buy more and/or bigger transformers than you think you'll need. You
will add more lights. Overbuild the power supply, or leave room for expansion. Consider separate transformers and lighting groups. Volt lights can't be dimmed, but you could set up your system to allow more and less light based on how many groups you have on. I have five in my yard, which provide everywhere from very subtle ambient light to land-your-helicopter-here. Run the wiring such that you leave plenty of slack to move the lights around, like by a lot. Coil up several extra feet of it, bury the coils in mulch. You
will move lights, and add lights, as your landscaping grows and changes. Use the water proof connections Volt supplies, but solder all those connections first. Take the time to do this seemingly unnecessary step (though it's a real pain). Doing that this time around has made this one of my many attempts at yard lighting 100% reliable, finally! All other forms of wire connections will fail, or at least compromise the brightness. Soldering is worth the trouble. And use 12 gauge wire throughout. You won't save much using a smaller gauge. 12G will give you the best results, brightest light.
If the PB is to run some of your circuits, have him add extras. Expansion, expansion, expansion. I went from one circuit to six, and still wish I had room for a couple more. I run garden lights, bistro lights, patio lights, flood lights, a bug zapper, a fountain, some citrus tree heaters and more. Your system will expand, putting extra wires in now will pay off. Or if he runs wires in conduit underground, double or triple the size of the conduit so you can someday pull more wires through yourself.
Music
No specific advice about equipment. My setup is pretty simple, just two overheads. But here is what I first did wrong. I placed them where everybody could hear them. But not everybody has the same idea of what the volume should be. While sitting at the table, I'd get constant requests to turn the music down. To the point where it could barely be heard at the table, and not heard at all anywhere else. I ended up moving the speakers elsewhere. Your multiple zones idea is the way to go. And/or increase the number of speakers, and plot them throughout the yard. Doing so will allow better coverage at lower volume, as well as more volume when you need it. Mount speakers facing away from primary conversation zones.
BBQ
Your plan sounds fantastic! Be mindful or plan for smoke. Keep the kitchen away from the dining area, or factor in ventilation. Add plenty of lights for the kitchen.
All that for only 2¢!
Just keep in mind: any stone work that penetrates the water (this goes for stone on wall and spa, too), can turn into a cleaning problem. Read here about effervescence. It leaches out of, and collects on, stone that is subjected to water and evaporation and is not fun to clean. That's why there is edge tile: a nice smooth, easy-to-clean material. Stone descending into water is a very nice look, just be aware of what you're getting into if your pool has a lot of that.
