The subject of throttles is a hot button topic here for a variety of reasons. Please excuse the vulgarity and personal attack posts in this thread. The forum is mostly civil with a lot of good folks providing useful information.
Yes, PAS 1 thru 5 simply adjusts the amount of motor assist based on rider input. It can be either torque or cadence depending on the type of sensor used by the bike. Torque sensors read the amount of pressure being exerted on the pedals where as cadence measures the speed the crank is turned.
Mid drives can have smaller motors because they use mechanical advantage gained by the gear shift mechanism. Rear hub motors are constant torque and don't have this advantage. Higher wattage hub motors are often used to compensate.
In general, mid drives are better on hills but this often depends on the bike. You've got the right idea by test riding. Every bike is different and the more you test, the better the choice you'll make when you do buy.
Electronic shifting is definitely worth looking into. If you find a bike you like that doesn't have it, the feature can be added to almost any bike. Many conversion kits are available such as these from Archer:
Electronic shifting systems for every bike. 100% compatible with any rear derailleur. Any number of gears. SRAM, Shimano, TRP, Campy, Box. We work great with everyone! This is the only electronic shifter you need for your bike.
archercomponents.com
I installed them on all three of my bikes. If you're at all handy with tools, the conversion takes about an hour with no special tools required.
By all means, play around with the forum search function. You're sure to have more questions. We were all new to the sport at some point so don't hesitate to ask!