17 days is time to take in sights in Chiang Rai too
Wat Rong Khun a must see.
Chiang Doi for a hike and some nice mountain views.
You can rent a car and do the whole loop - up 107, stop in Doi Mae Salong and Doi Tung for the Queens Palace, across to Chiang Rai and Tachileak, on to the Golden Triangle and the Opium Museum. Chiang Khong for an overnight on the Mekong river. Loop back via 118 with a stop by Singha Park.
Waterfalls, Nat'l Parks, many restaurants enroute.