... how does one do the following on a Tesla (or something like the Jaguar I-Pace for that matter - another vehicle I'm interested in checking out): turn on the headlights, heater / defroster / a/c, cruise control, turn signals, etc. Are there no longer manually operated dash controls for stuff like that?
Headlights - automatic, work really well in my experience including auto-dimming high beams. There's a menu in the screen if you want/need to control lights manually, one tap takes you to that menu so it's not hidden deep in the menus.
Heater/defrost - there's a thumbwheel on the steering wheel that you can set up to do different things. Mine is set up to control fan speed, so just rotating the thumbwheel will activate the HVAC system to whatever it's set at. Most people use the Auto settings to control temperature and where the air is blowing from, and for fan speeds as well. I prefer to set those things myself, but the option is there to do it either way. No need to take your hands off the wheel. For the defrost, there's a "button" location you tap on the screen to turn on the rear defrost, and a different one that turns on the windshield defog on the first tap and defrost on the second tap. You do have to take your eyes off the road for that one, but I find that no different than my last car.
Cruise - stalk on the steering wheel activates cruise/autopilot, and deactivates it. Pretty simple learning curve for that one.
Turn signals - just like any other car you've ever driven.
Most stuff is controlled through the screen, but a lot of stuff you only have to set up once and then generally don't touch again. The car saves your setup to your profile, and you can have multiple profiles for different drivers, so mirrors/seats/etc. adjust as you select the different profiles.
Try one out, I bet you'll like it. Even the one-pedal (ish) driving feels very natural to most people with just a few minutes of seat time.
Good luck with your decision-making!