Thank you so much for all the replies. I'm having second thoughts about my first electrician choice (they did a great job on my solar but they seem less knowledgeable about EV chargers). I'm leaning now towards just getting a 14-50 installed - I think that's the most future proof way to go. I think at some point all the charger ports on EV's will be standardized (although who knows - Apple still uses lightning cable so maybe Tesla is a big enough gorilla to have a proprietary standard and everyone else will have to add adapters).
Thank you so much! You've cleared up some of my misunderstandings. I'm looking forward to ordering my Model Y soon.
If you want to install two or more circuits for EV charging using a sub panel, the feeder to the sub panel needs to be designed for continuous loads. For example, if you install a Tesla Wall Connector using a 60 amp breaker and a NEMA 14-50 (or 6-50) on a 50 amp circuit, which will charge one car at 48 amps and another at 40 amps, the load calculation for the feeder needs to consider the load as a continuous load of 88 amps.
If you install the Wall Connector on a 50 amp breaker and the NEMA receptacle also on a 50 amp breaker, the cars will both charge at a maximum of 40 amps each and the load calculation for the feeder news to consider the load as a continuous load of 80 amps.
Note that such a circuit needs to be installed in conduit using THHN/THWN wire. The sub panel *could* be wired without a neutral since both loads would be strictly 240 volt loads, however I would install a neutral as it might be convenient to install some 120 volt circuits to the sub panel for other devices. And depending on your local inspector, he or she may require a neutral. In the event any additional circuits were installed in the sub panel, it would need to be fed with a larger breaker and larger wire to serve those additional circuits.
Personally I have two Tesla Wall Connectors for my Model X Plaid and Model Y LR with individual runs of #6 AWG THHN/THWN wire (in PVC conduit) run to my electrical panels. After spending over $200,000 for the cars, it did not make any sense to do it any other way, and was relatively easy as the panels are in the garage.
However, my son, who is on more of a budget that I am, shares a single Wall Connector on a 50 amp circuit for his Model 3 rear wheel drive and Model 3 Performance. Just requires a little coordination between him and his girl friend.
Using a sub panel and installing more than one circuit off the sub panel, installing two circuits back to your main panel or panels without a sub panel, installing a single 240 volt circuit with 20, 30, or 50 amp receptacles, or installing one or more Wall Connectors to the afore mentioned circuits depends on your particular circumstances and budget. I know of a person who only has 100 amp service in his house and he installed a 30 amp circuit (using #10 Romex (non metallic cable)) to a Tesla Wall Connector (charges at 24 amps) and has no problems. Car is always charged in the morning since he gets home about 6 PM. I think most people overestimate their requirements, but some have unique requirements were they need to charge faster than 24 amps. Only you know what you need.
I suggest using a licensed electrician for such electrical work, and getting a permit if required.