Hey, welcome to the forum! Answers to your questions:
1. Yes, the HC250 is last generation, and was replaced by the EA3/EA1
2. The HC250 can do Spotify Connect, but only if there is another more powerful controller in the system (HC800, EA1/3/5).
3. Updates to software are only possible by a dealer, using the Composer Pro software. Also, the HC250 is not supported on OS3 I'm afraid.
4. Unlikely I'm afraid, only Dealers can add and remove drivers
Sorry you have had a bad experience with your dealer, there are some great folks on here who might be able to help you out remotely
1) Hc250 cannot be in a project if you want to go to OS3. So it works, it works up to OS 2.10.6. You can go to the C4 site or google Control4 OS3 to see the changes. its a very big UI overhaul and there are some new features. Do you need it? that is up to you to decide
2) Spotify has eh c4 integration, most control needs to come from the spotify app. I dont use spotify so others will chime in with more details
3) You need a dealer to upgrade OS, but as I mentioned above, OS3 cannot have an HC250 (and a few other pieces of hardware) in the project. So you'll have to replace the HC250. A remote dealer can help sell you the new controller, help you ID it to your system, then upgrade you to OS3
4) Depending on the complexity you can do it in Composer HE but you cannot add mini apps. Depending on the TV (if its Android based) you may be able to do "watch > Youtube TV" and get it to launch straight to the app. That would require a dealer. Otherwise you should still be able to access your main TV menu then manually pick YouTube TV even in its current set up? There should be a "watch > something" available, the something being the TV. Some call it Living Room TV, some may just call it TV, others may call it by the brand name like Watch > Sony etc. So hard to know. It may not be visible, but if its in the project, using Composer HE you can go into the navigation in the room, go to the devices shown, show it, then be able to get at least get to your TV main menu to manually select youtube tv
