Thanks for your feedback!
Panniers has me a bit confused. If you use the reaction effect, do you get +1 card? I'm also not sure why it returns a card rather than simply trashing it. That's a valid choice, I'm just not sure what it adds really. I think the on-play effect could be buffed.
Yes, you get +1 card. Compare with Caravan Guard.
Returning adds a subtle difference to the game, because cursers will continue working.
Law, by contrast seems too weak. For comparison, consider Catapult. Catapult not only gives $1, but also provides a benefit upon trashing copper.
You might be right. I think reducing the cost requirements to $2 and $3 could be a nice fix. Now you will draw terminally while trashing estates. After that you need to feed it silvers or something.
Midway seems pretty interesting, although not strong. The reordering ability seems like a fairly important part of what makes it good.
If you get two right, it's at least a cantrip, or Necro if you need the actions, or Moat if you have enough actions. So at least you get choices. If you get three right, you can choose between Village, Lab, Smithy and +3 Actions. If you get just one right, you're crying. Your deck composition and tracking will both matter.
I have issues with Alderman. It seems kind of slow to play with, and without good reason. Most often, you reveal at least one action, and now Alderman is an expensive village, hooray. Maybe you reveal a victory card and can play your Mill, making Alderman a double village. But so what? I'm not sure what Alderman is really for, but honestly it sounds weaker and less interesting than a vanilla card that just says "+1 card, +3 actions".
It rewards decks with several types, that's what's supposed to make it interesting. Also you need actions in your hand and in your deck. Action-Reaction, Action-Victory, Action-Attack, Action-Duration, Action-Reserve, Action-Traveller... It might be too narrow to be good in most kingdoms though. Reserve or Duration heavy kingdoms seem the best.
I also have issues with Prowler. Mainly it's a glorified woodcutter. Or if you're buying treasure, and have extra buys, it's a glorified treasure. I think you could do more with a simpler card, e.g. an action/treasure that only gives +Buy if you play it in your action phase.
Woodcutter is a fine card, and this is certainly different enough. The top part is better than Woodcutter. For the bottom part, maybe it doesn't need to discard itself? If you gain several Treasures, you could play them all. You would be able to buy all the Capitals though, getting +$1 more for each one! (But then you would be in crazy debt, so I doubt that's a good play most times.)
Even without that change, this card is crazy when you buy Fortune (EDIT: not really, you won't usually have any $ left for it to double). Also very good with Idol, Scepter and Crown.