First, a minor point: If you want to emulate the look and feel of the official cards, go Times New Roman for the interior text. That font is great for the name of the card and its type, but hard to read when it's used for the instructions.
Another technicality: the official cards all have a horizontal line dividing "on play" behavior with behavior that happens at other times (e.g., all reactions; "while in play" for Goons and Lighthouse; "setup" for Young Witch and Trade Route). This is useful whenever there is doubt about which parts of the card get doubled with Throne Room.
Ok, enough of the nitpicky stuff.
Servant's Quarters is quite interesting. My concern, I guess, is that it will be interesting on too few boards. How often are cards discarded during the Action phase? Hamlet, Horse Traders, Cellar, Warehouse, Secret Chamber, Young Witch, Tactician. Can't even think of any others off the top of my head. This probably is not enough to justify that card behavior. That said, when it *does* activate, it's really cool. With some finagling, you could use it to get double Tactician turns. (Play Village, play Tactician, discard Servant's Quarters, draw Laboratory, play Laboratory, draw Tactician + one other card, play Tactician.)
However, here's a question: Do you mean that the Servant's Quarters should be discarded from your hand, or is it not important where it's discarded from? If it counts if the card is discarded from anywhere, suddenly now it activates when Adventurer skips over it (because those set-aside cards get discarded when Adventurer has found its two treasures), when Harvest turns it up, when you choose the discard option on Navigator, and so on. Offhand, I can't think of any problems with this, but you'll want to consider all the official cards very carefully for rules complications or broken game states before allowing this. But if it can work that way, it might be a much more interesting card. But I would still expect that particular feature to be usable on only a minority of boards, so it's a good thing that it does more than that too.
Still, the card needs to be usable on ANY board, not just these. And if all you get is +1 Card, then that is strictly worse than nothing. Maybe add a +1 Buy onto it? I'd still be worse than Herbalist, but at least then there would be situations you'd want one.
Any reason you don't want to gain a card up to $4? Workshop does and only costs $3. A one-shot Workshop would be fine at $2. I know (and appreciate!) that you are concerned about powering up your cards too much, but honestly I think even with this boost, Pauper's Feast would still be generally undesirable. But it would at least be "better than nothing" in a wider variety of situations. It's an okay consolation prize, for example, in Gardens and Conspirator races.
I really can't think of any non-contrived situation where it's worth using a buy and a subsequent action just to get a Silver. Why wouldn't I just buy nothing? Then, on the turn where Pauper's Feast *would* have turned up, I'll have both a card and an action I wouldn't have had -- and, therefore, be better able to raise $3 naturally AND preserve the chance I'll be able to raise MORE than that and buy something better.
If you really don't want to raise the limit to $4, then Davio's idea of gaining TWO $3 cards is pretty good. If you don't like that either, then I'd suggest not only +1 Action but +1 Card as well. Still weak, but at least then I wouldn't feel like it's basically ALWAYS a bad buy.
This one's fine. A weaker Pawn in exchange for attack immunity is a fair trade. But it's unfortunate that in non-attack games, which are common, Pawn is strictly superior. If you can offer a nuance that Pawn doesn't, that would improve the card. It doesn't even have to be something particularly good, just something slightly different.
Choose two: +1 Card, +1 Action, +1 Buy. The choices may be the same; if they are, discard a card.
Come to think of it, that particular version would make it another card that could activate Servant's Quarters.