More info... A quick google on dressing up as a geisha turned up this company:
[Makeover Plans]Yumekoubou-Maiko Makeover Studio
Also, going to Koya-san is definitely possible as a day trip. It's about an hour and a half from Osaka's Namba station, maybe a bit more. Getting to Namba station from Kyoto will take a while too, at least an hour I'd say. Still, if you leave early in the morning, it's certainly gives you plenty of time to explore Koya-san. For comparison, Nikko is about 2 hours by train from Tokyo, so it's not much farther from Kyoto to Koya-san. What you may want to do is head down to Koya-san, stay the night at a temple, and then hit Nara on your way north again the next day, or head west to your destinations on Shikoku, etc. Or maybe spend a night in Nara or Osaka to cut at least an hour from the trip.