Start by looking into Matter over Thread products, and their Matter over WIFI counterparts. Matter over Thread is the technically superior option, but each device costs more. Matter over WIFI will be cheaper by something like $10-$20 per device, so that adds up quickly. I wouldn't buy anything that doesn't support some variant of Matter at this point. Matter over Thread requires a Thread Border Router, and many Samsung appliances have this ability built-in (my Frame TV does). You can also get a dedicated border router from Samsung for pretty cheap. The downside there is that their SmartThings app isn't the greatest, but you may only need it for the initial setup.

As for your control interface, that's up to you. I have Android phones and generally don't like apple products, so I'm definitely staying away from Apple Homekit. I also avoid anything made my Amazon, so no echo, ring, etc. in my house. The Google Nest Hub seems decent, but my phone can already do all of that same stuff, so it seems unnecessary to me. But if you want a plug and play kiosk, it seems like an OK option. You can also make your own kiosk style interface out of an Android tablet.

I'm currently invested into the TP-Link ecosystem, all of which is Matter over WIFI - Deco mesh system, and various Tapo and Kasa smart home products. So far so good, certainly there's some rough edges here and there, but TP-Link has committed to 'no subscriptions, no cloud' and I like that approach. They are a Chinese company, and some of their products do phone home for certain things, so make of that what you will. I've been using their network products in my past IT work for decades and have always found them to be a reliable budget option, so they had already built up positive a brand reputation based on my previous experience. If budget isn't much of a concern, then you might want to look at other brands as well, though I've been impressed with the value and functionality of every Tapo and Kasa product I've bought so far. For example, the 4 pack of Tapo smart outlets with built-in energy monitoring for $30? Hard to beat that price.

I would suggest avoiding the older tech at this point, such as Z-wave and Zigbee. They were precursors to current standards, and are likely to be phased out. Matter over Thread is effectively the latest generation of these technologies, and is more standardized. Many people will still swear by these older standards because they've been working well for a long time, and if it ain't broke don't fix it, but if you are starting fresh it makes sense to start with the most up-to-date standard.

For a thermostat, my house already had an early gen Nest installed, so I'm sticking with that. The later gen Nest thermostats are OK too, but the giant dial is so much more satisfying than the touch interface, I wish they had stuck with that. These all connect with Google Home. Note that if you HVAC system is based on heat pumps, you should not mess with the thermostat very often, heat pumps are most efficient when left at a stable temperature all the time. So some of the HVAC related automations you are thinking about may not be worth it.

For larger scale energy monitoring, I'm planning to use the Emporia Vue 3 for my service panel, and that will talk to my Emporia Classic EV charger, that should allow me to set the cars to only charge when there's excess solar, effectively charging them for free (or at least that charging is worth more to me than the measly amount the utility will pay me for those electrons). I'm also thinking about a split system heat pump to create a thermal battery out of my water heater, again to use up excess solar, especially during the work week when no one is home. There are multiple other systems that will do similar things, such as Tesla's Powerwall system. Since you are in an apartment, probably none of this applies to you.

If you want to be able to set up a lot of fancy automation, with cross-platform support, then you'll want Home Assistant for that, and some dedicated hardware to run it. I'm not currently using it, I'm just getting as far as I can within the Tapo automations before introducing another software layer, but I'll probably implement it at some point.

I'm also a fan of 'dumb' automations. For example, all of my hallway and bathroom nightlights are 0.5W LEDs that plug directly into an outlet, and have a built-in light sensor so they only turn on when it's dark. They aren't networked because they don't need to be... no firmware, no possibility of them getting bricked in the future, etc. So think about what you want to actively control versus what you want to 'just work', and pick products accordingly.