If you're going to plan to install a Tesla Wall Connector, you don't need the neutral. But, if you ever wanted to install a relatively common 14-50 outlet in the future, you will need the neutral. It is better in terms of labor cost to have them run the hot, hot, neutral, ground to the 14-50 setup and disconnect/cap the neutral and leave it in the wall for future considerations. I don't know how much of a difference in cost it would be, but I could almost guarantee it would be cheaper than having an electrician come back a second time in the future and try to run the neutral through to the outlet.
If you're going to install a 6-50 or 14-50, this is a 50 amp breaker, that's code for sure. If you're going to upgrade to a HWC in the future, the breaker can be changed to 60 amps *IF THE GAUGE WIRE ALLOWS THAT MUCH AMPERAGE* and then yes, your HWC will maximize at 48A.
And yes, the current Gen2 mobile connector is limited to 32A regardless of the outlet, wiring, or breaker.
The key in this is if you're looking to eventually upgrade to a HWC and charge at the maximum 48A, you should have the proper wiring installed that can support it.
Circuits on 50A require 8 gauge wire. Circuits on 60 (maximum 65A) require 6 gauge wire. Some people choose to install 4 gauge wire for less resistance losses. There are some other perks of using 4 gauge wire if you try to powershare between multiple HWC in the event you have multiple Teslas that need to charge simultaneously.
Personally, if I do install a HWC, I am going to plan for 6 gauge wire and run it on a 60A breaker and hardwire it. But, another option could be to have the 14-50 and use your MC. You *CAN* install the HWC with lower amperages but you have to be sure that it is set and installed properly - you COULD remove the 14-50 you install, install the HWC, and charge at 40A without changing the wiring or breaker, as the whole circuit is already set for 40A continuous pull. In this case, I would use 8 gauge wire unless the cost difference was negligible.
Just for reference in terms of energy, before some efficiency losses are factored:
32 amps * 240 volts = 7680 watts per hour
40 amps * 240 volts = 9600 watts per hour
Your Model Y has around a 72.5 kW usable pack, so that means it would take around 9 1/2 hours to go from completely empty to completely full. Most people only charge to 80% for typical use unless they need it, which would be around 58 kW.
With the Mobile Connector and 32 amps, you'd charge from your 0% to 80% SOC in about 7.5 hours.
With the HWC and 40 amp charge rate (50A circuit), you'd do the same in 6 hours.
With the full HWC on a 60 amp circuit (charging at 48A), it would take 5 hours.
Only you can determine how quick you need to charge. There are benefits to charging faster - like time of use billing from your utility, where you get super cheap rates overnight for example, so you want to charge as much as you can from, say, midnight until 6 AM.
As someone that only drives around 30 miles per day, I *personally* don't really have a need for anything really beyond a 6-20 or 14-30, so it all depends on what your driving habits are, and how long you have to charge before you need to use the vehicle again.
