1. The Drink seems very low, currently at 9. I've got brew on repeat again - not enough dwarves, brewer was multitasking, had to mod his skills. I have no context for how to scale the numbers for food (at 66), seeds (at 25), and drink - is that enough drink?
I like to keep my booze at 5 units per dwarf, minimum. So for 20 dwarves I would not be comfortable with fewer than 100 units of booze on hand. When the fortress is mature, I'll aim much higher.
5. I get a lot of "cancels Plant Seeds: Needs plump helmet spawn" messages, but the kitchen shows 13. From searching the forum, that appears to be an artifact of the way seed containers are moved around - do I need to worry about this message, or can I ignore it?
Disallowing barrels in the seed stockpiles can help with this. Also, if you aren't already customizing your food stockpiles, you should start doing that. Try a small no-barrels seed stockpile by the farms, and no seeds allowed in any other food stockpiles. You'll still get the cancellation spam when they take the bags out to gather up seeds, but it won't be quite as bad.
6. In the kitchen screen is red disallow and blue allow? I hope so ... please have the dev team change those to red and green :-)
I'm not colorblind myself, but I've been led to believe that red/green is a bad combination for people who are. Maybe that went into Toady's decision. In any case, it's unlikely that anything we write on this forum would influence the development of the game. Toady rarely reads this stuff (he's too busy coding).
9. Since setting up my stone fall traps, I have a huge pile of rat corpses at my entrance. How do I clear them, and are the traps still good?
Are they actually giant rat corpses, or just rat remains? They're quite different. Remains are vermin that have been killed by cats, not by traps. Corpses are dead creatures that may be large enough to butcher for meat.
If a stonefall trap is triggered, a job will be created for someone to reload the stone. This is automatic, so you don't have to do anything about it. Of course, the drawback is that if a bunch of goblins hit your stonefall traps, your civilians will walk right up to them.
Management of corpses and remains can be handled in various ways. If they're just vermin remains, you can ignore them. They'll go away on their own eventually, and vermin remains don't produce miasma (they haven't for a very long time). If they're corpses, then they may start to rot and produce miasma if they are underground (they won't produce miasma above ground). If they're butcherable corpses, and if they're sufficiently close to a butcher's shop, and if you have a dwarf with the butcher labor enabled, then they'll automatically be butchered. However, if any of those conditions are false, then they won't be.
So, for corpses that aren't automatically handled, you have a couple choices. You can make a refuse stockpile, and dwarves will haul corpses there. Or you can make a garbage zone and dump them manually. (For either approach, you may also have to enable the option to deal with "outdoor" refuse --
o r o if I recall correctly.) The problems with refuse stockpiles are: (1) they fill up way too quickly (no bins/barrels -- everything takes one tile); (2) dwarves may put things there that you don't want them to; (3) some items decay when stored in a refuse stockpile, but not when stored on a regular tile. I prefer to manage my corpses with manual dumping, to a garbage zone that is close to the butcher's shop, and also under a raised bridge. Anything that can't be butchered, eventually gets smashed.