Longtails out of Krabi, night temples in Chiang Mai, the two markets outside Bangkok. Tell me the shape of the trip and I'll price every leg live.

One night a year, on the Lanna full moon. The release everyone photographs is ticketed and 30–45 minutes outside the city - not the free one in town, which runs the same nights and is worth doing as well.
Thailand waives the visa fee for Indian passports on stays under 60 days - you land, you get stamped. We still check your return ticket, funds proof and hotel confirmations before you fly, because those are what get people turned around at immigration.
The one rule worth remembering: June to September, book the Gulf, not the Andaman. Same country, same week, and only one of the two coasts will run its boat days.
Both coasts behave. Yi Peng lands on November's full moon, and Chiang Mai sells out six months out.
Warmest water of the year and thinning crowds. Songkran in mid-April is worth planning around, either way.
Krabi and Phuket get rough seas and cancelled boats. Koh Samui, Koh Phangan and the Gulf stay fine.
Rain easing, everything green, prices at their lowest right before the season turns.