You could part make the batters for freezing (but I can't see a whole lot of point), fats don't freeze well and ice crystals tend to rupture them and make them weep, so you could just work with the flours and sugars (but thats hardly a time-draining process, so like I said, prepping and freezing would be fairly pointless).
Increasing the shelf life of you brownies and cookies isn't too difficult, but take into consideration:
1) Starches stale; increasing the fats and the sugars will reduce that, also an emulsifier will reduce staling too; think about intergrating egg yolks into your mix. But becareful as this can affect texture too.
2) Fats oxidise; if your batter is very high in fat, then you need to protect them from air and light; otherwise they can create some fairly stale flavours.
Also lactose degrades (milk and cream) and bacteria can infest anything not refrigerated (unless high enough in acid or sugar to make in inhospitable for bacteria), but refrigeration will also increase staling (massively) but could be regelated later (by reheating).
I would reccommend starting as soon as you like but using mixes and batters high in sugar, low in dairy (using shortening instead of butter) adding emulsifiers when mix is low in sugar and fat, wrapping everything (individually) and refrigerating everything- and if they go stale; reheat on the day you want to send them (just past gelation temp between 68-80degC).
Pastries may be a bit of a problem; my advice would be to avoid butter as much as possible and go with your more manufactured shortenings; they tend to freeze better, but unless you've got a blast chiller, there still may be freezer damage. Long-term refrigeration is never a good idea with pastries, and usually produce stale flavours quite quickly (oxidising fats).
Try to think what else is in your freezer too... fats love to absorb oderates from the air, so other food may affect the flavour of anything frozen.
Hope that helps.