I would bake in advance and then freeze them. Do you have to make 800 decorated cookies, or are some of them things like chocolate chip or oatmeal raisin?
easiest - make sugar cookie dough, wrap well and freeze.
When ready to decorate pull them out of freezer the night before to start decorating.
Quick and easy decorations - use a brush and put a swipe of carob? syrup over them then throw some sprinkles, etc. on them.
P.S. Oatmeal cookies - a no-no for freezing (oatmeal absorbs the moisture)
I think I'd do a combo of freezing and recruit helpers. Know any older children or younger teens? Girl(or guy) friends you could trust with baking too?, a couple ovens would better than one. Good luck, let us know how it turns out!
Wow that's a lot of cookies! But for a good cause!
If they don't have to be decorated I would do a variety of chocochip, gingerbread and sugar, roll the dough into balls freeze on a cookie sheet and then pack into bags once frozen.
Then when you are ready to bake just pop them on a cookies sheet and bake away, just like the frozen ones from the store, but homemade!
spritz cookies are fast and easy and look very festive. Definitely freeze, i think its the only way. I would make all dough first then have a baking day. Sounds like this is a donation, if it is make it the easiest on yourself. For festive looking sugar cookies without all the work, scoop balls of cookie dough and roll in sprinkles or colored sugar before baking. Also, if you can find one of those doughs that you keep adding other things to, to make a new type of cookie, do it. Then you can make a boat load of dough and just keep changing them up. If you are doing cutouts just decorate with sprinkles, maybe to a couple per tray of fancy cookies, but otherwise keep it simple and keep your sanity.
i think the spritz is your best bet-you can do so many shapes, drizzle with chocolate, sprinkles, put cherries in the middle, what ever. and i love the idea of having a cookie baking/decorating party-tis the season right? (maybe have gingerale or sparkling grapejuice instead lol) why not make it fun instead of stressful. good luck!!
If this is a donation, you want them to be nice, of course, but you're DONATING 800 COOKIES (!), so keep the work to a minimum. One of my best friends does a lot of work in a homeless shelter and soup kitchen. Based on my conversations with her, homemade chocolate chip cookies would be a super treat and MUCH appreciated by the recipients. 
These kind of cookies (drop cookies) can be mixed up, then using a cookie scoop, scooped into cookie dough balls (WAY faster than "rolling" them into balls), lined up on a cookie sheet, thrown in the freezer until firm, then boxed up & stored in the freezer.
On baking day(s), just pull out the dough balls (do not thaw) and bake.
I used to do 300 cookies a day this way ... every day .... and baking time was minimal.
Does the shelter have a commercial oven and if so, will they let you come in and bake? That will REALLY speed it up. You could sell the idea as "warm, fresh cookies" for their clients. For example, I can fit 24 cookies on an 18x26 baking sheet x 5 sheets in the oven all at one time = 120 cookies per baking batch (15 minutes per batch), so it would take you less than 2 hours to bake in a comm'l oven, if the dough balls were already made up and ready to go.
I agree, 800 decorated cookies....a nightmare! I'd say do something easy with sprinkles. If you have to decorate, I'd go the RBC or MMF route. You can buy some stuff called Satin Ice, tastes good. That would go so much faster. Please let us know what you end up doing! There's lots of threads on freezing.
Definitely spend a day mixing up all your cookie dough, and do all the baking on a separate day. I do that with my Christmas cookies just for family and friends, and I do about 20 batches of cookies and a dozen cheesecakes.
It would be great if you could use a commercial oven someplace where you could put lots of trays in at once. If you were nearby I'd offer to help. Good luck, and good for you for doing this for others.
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