I just put 'fleet supercharger' into destination on drive
Clicking on the Supercharger Pin then offers NAVIGATE, and will pre-heat the battery en route for optimum charging when you get there. But I think that presupposes that you know where Superchargers are (but as you say, the Supercharger button whelps to point them out). Alternative is just to put your final destination in and then if not enough energy to reach it then SatNav will route you via a Supercharger. That's useless if you don't need a supercharger to get to destination ... bu do need some extra charge for WHEN you get there ...
You could try the Voice Recognition : "
Navigate to XXX and make sure I have at least 100 miles of range when i get there" ... athough I'm pretty sure that's not even in V10
although the Taycan voice recognition is a lot closer to actually being able to do that sort of, useful, trick. Your Model-3 will put on twice as many miles at Supercharger in the time that Taycan can at a ultra rapid charger (assuming it can find one ...) and you've got a bit more cash in your pocket ... what was the question again?
All rather hit and miss, but when we got back to car we manually stopped the charge at 80%
You could set the CHARGE LIMIT on the dash, and that would give you accurate completion time (which would then change when the a paired car left), but once reached you would have to pay "fine" for occupying a stall but not charging, so apart from not being a good citizen
setting CHARGE LIMIT to 100% ... or 90% - even if you don't intend to charge that high - does give you some leeway.
You can also put your next destination into SatNav to get a feel for how much energy you need (maybe adding 10% for "contingency") (You have to press "resume journey" or something like that to get it to show you the (negative, to start with) battery position for the remainder of the journey).
I think it is helpful to know how fast the car charges, so you might want to make a note at 5 minute intervals, and incorporate that with getting to a Supercharger to start charging at 10%, or lower. If you have TeslaFi you can extract that "knowledge" from the Graph it displays (or look at Help : Raw Data to get some more specific figures if that is your sort of thing)
Knowing what to expect means you can just watch that the car does indeed ramp-up to expected kW, in the first minute or so, before you wander off for Pee and Coffee ... and also when it begins to taper, and by how much. I've had stalls that were bust and were on much lower power than normal - just moving to another stall fixes that. You probably won't care for the slightly longer charging time from 70% to 80%, but you definitely would for 80% to 90%
If another charger is available on your journey then journey time is shorter to drive-faster and charge-longer and stay out of Taper ... you do need an unoccupied stall that is working, but if you are going to have to stop anyway ...
Whilst getting a bite to eat you can use the Phone APP to see how the charging is getting on, and when it speeds up (as the paired car leaves)
All that is more complicated if need running-around-charge when you get to destination or until home charger installed etc.