I know I am super late to this thread, but for any future lurkers:

The best option for something like this is to get a cheap thrifted bike, and slap a mid-drive ebike kit on it. I got a bafaang kit for mine, and it costed about $700, and the bike itself $50. It took an entire day and all my friends beating the shit out of said bike to get the upgrade done, a bunch of post-work as well, but it made me much more familiar with what I need to do for future repairs.

A used Aventon abound would cover most of that. I paid about $2K for mine new a couple years ago, so used should be at least in the ballpark. I have about 3000 miles on mine now.

Top speed about 24mph with current firmware, but you also have to replace the freewheel, the stock one is 14T which isn't small enough, the drift maniac freewheel on Amazon is 11T and direct replacement.

I have panniers plus the front rack, I regularly do the grocery run with it.

Not class 3, but class 2+, it's throttle will go to 20mph but with the freewheel you can pedal faster, I regularly do. With lights and such I tend to average around 19mph.

Plenty of torque for a trailer, I have one that's rated to 100lbs capacity. I've overloaded it to 120 (3 40lb bags of salt) plus groceries in the panniers. I've probably carried 200lbs between the bike and trailer. Not at 24mph tho ;)

Removable battery, with just me at about 200lbs dressed at top speed I get about 30 miles of range, but I don't push it that far.

Standard lower end bike parts, like anything else you'll find in this price range. Shimano Altus derailleur.

Handlebar folds down, but it's a big bike, 20" cargo style. Somewhere around 100lbs with racks and panniers.