So long as the supply transformer has sufficient amperage and the wiring of the chime setup is adequate to minimize voltage drop, adding other units in parallel works well. I have not had an installation using a diode field-installed at the door button. For terminology, using the terms "bell" and "chime" interchangeably tends toward confusion.

I recommend 18 gauge wiring for chimes. Some installers use 24 gauge telephone cable. The chimes often sound very weak with 24 gauge. Some parallel the 24 gauge conductors for better performance. I have installed three chimes on a 30va transformer. Never have installed four on one control circuit. If the results are not good, search for an 18 volt transformer. Here is a link that might be useful: Nutone

So I’m thinking that the metal backplates won’t work because you’d have to drill though them to mount the SkyBell. I wonder if this vinyl mounting block would work. I could paint it to match the wall or the doorbell. Would it work to drill through it though? https://www.lowes.com/pd/Builders-Edge-4-5-in-x-6-25-in-Paintable-Vinyl-Universal-Mounting-Block/3046029?cm_mmc=SCE_PLA_ONLY--LumberAndBuildingMaterials--SosVinylSiding-_-3046029:Builders_Edge&CAWELAID=&kpid=3046029&CAGPSPN=pla&k_clickID=12372e30-4788-5a68-3b35-000024defbcc&gclid=Cj0KCQjwuafdBRDmARIsAPpBmVWGLOQ9leMtTMdYiJTGwqQOcSTKSgNLeEKQ4D7WZTgvelN83ZiAnT0aAlMcEALw_wcB

I have a Nest thermostat and Nest doorbell. TLDR: I like them. They work and were easy to install and integrate. If you can, connect them to your 5ghz wifi (more stable and stronger connection). Thermostat: I was initially worried about if I would actually get use out of the thermostat because I am someone who really dislikes the idea of a thermostat automatically changing its temperature based on activity or other "smart" functions -- I like my temperature to be steady and comfortable. So, I do not use the Nest's automatic schedule and just made a custom daily schedule like any normal thermostat can do. So obviously I am not utilizing the main feature most people get a Nest thermostat for. However, I have found it useful for being able to see a daily history of use (ie: how much the system uses heat or ac), plus I now have humidity control (steam humidifier), can change the temp when I'm away from the house if needed, and I love that from a distance I can look over at the thermostat and it actually lights up and I can see what temp it is at. There are a ton of other useful features that I know are saving on heating and cooling costs and I did notice a difference in comfort in my home. Doorbell: I really like being able to see when deliveries happen, I can watch wildlife from time-to-time, and avoid those door-to-door salespeople. I also get an announcement of who is at my door when they ring the doorbell, ie: "Mom is at the front door". It was very helpful to have when a service company arrived to my house early (before I got home) and I could talk to them to tell them I was 5 min away.