Rough itinerary will be
Chiang mai from 25th till 30th.
26th and 27th local tour guide around chiang mai. (elephant ride, golden triangle etc. or maybe even just wander around the area by our/myself)
28th night is the yee peng festival, get some flying lantern and enjoy the festival. (cant wait!!!)
29th might(or might not) take a day trip to burma/nyanmar or chiang rai. (its like 2-3 hours trip from chiang mai)
Totally flexible, except 28th night