For question one, I'm pretty sure you can use any of them. And since you're billed on the actual quantity of power used, it'd be nearly indifferent. Not 100% on this though.
For your second series of questions, it sounds like it'd be pretty close to equivalent really, at least at first glance. I wouldn't mind someone checking my thoughts on this as I'm far from a math ****, I'm actually a writer lol, so I could be missing something.
I decided to approach it from the perspective of total time at first glance, just to see wiggle room there would be for charging.
3000/70 = 42.85 >> 43/10 = 4.3 >> 4 days of hotels, arriving on day 5 after 3 hours.
3000 miles, going 70mph = 42.85 hours of driving. 10 hours a day, makes it 4 days (10hr segments) and 3 hours of effort based on car time alone.
That would leave 7 driving units (hours) to account for charging across the 4 day trip, before it would trigger a new day, requiring a fifth hotel stay - assuming we have to factor in the charging times as actual driving time, which IMO is a questionable decision in this whole thing.
Referencing this graphic (
https://blog.carvana.com/wp-content/uploads/2021/07/EV_BlogInforgraphics_ChargingTime_v4.png) which was the first result in "tesla supercharger times", we can ballpark supercharging times at about 30 minutes. Note the graphic does say full charge from fully depleted, and I'd imagine that not to be the case in the event of a cross country drive but who cares. This is quick and dirty.
Model S gets a touch over 400 miles per charge, and we're driving 700 miles a day (70mph x 10hrs), so with charging 2x a day we'll effectively lose an hour per day of driving - though likely a bit less because we wouldn't be charging 0 - 100.
But again, quick and dirty number run here. That would put you at 8 hours of charging times, theoretically adding a new hotel stay, by 1 hour. If we were to get a bit wild, knocking off 7.5 minutes from each charge is all it would take to erase that hour, which I have no clue would be feasible or not. And in the real world I'd imagine 99% of us would just push that final hour to get to the destination.
Ballpark costs:
Model S cost and weight theoretically aligns it pretty close with a BMW 7 series. BMW 7 series gets 22/29mpg, I'm going to use 25mpg as the average for math sake. This may be upsetting to some, or not, I don't know or care really. I don't think it's fair to align it with a 40mpg civic that weighs 1500lbs less, and someone else can do this if they feel so inclined.
ICE:
fuel= 3000 miles @ 25mpg = 120 gallons of gas @ $3.4 (
https://gasprices.aaa.com/) is $408 in fuel.
hotel x 4 = $400
total = $808
EV:
charging = 100 kWh battery pack, at $0.25kWh supercharging rate = $25 for 0-100 charge. 8 charges = $200 (I'd suggest this approximately 1 $25 charge too high, since we were using approximately 7/8 of a charge per day, but again who cares)
hotel x 4 = $400
total = $600, or $700 if you needed that extra night. Or $800 if you felt like really relaxing while still saving $8
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(Feel free to check these numbers. There is a great chance I messed up somewheres. I did all of this on the fly while writing this out, so it's definitely possible and you wouldn't be offending me)