Lotsa tourist agents located at Khao San road but that's not convenient from BKK city bcos no MRT/Skytrain servicing that part of the city. Nevertheless u can find scatter agents around the city ctr too but abit pricy...compare to Khao San road.
Simple, just hire a taxi-lah (Only THB800!) & remind the taxi u don't want to goto those Motorised boat terminal but instead ask him to bring to those hand rowing boat terminal...Using taxi or agents, u still cannot bypass the so called "Tourist Stopping station" to watch gem stones or silk factory. This is a norm in every countries 

double checking,

LCCT to BKK, takes about 55 min to fly, right?

ahhh i will be on board alone, so gonna make sure that. 

Yes almost whole day the THB800 taxi ride (Nego kaw-kaw from thb1000) include bringing you to Damnoen Saduak floating market, Elephant & snake farm (I requested them to skip bcos my wife & daughter dislike all activities related to animals , Gem factory (A must for him to get petrol voucher! ), and on the way back to hotel, he even stopped & wait us on our travel around Wat Po & Grand Palace.

Too bad, the taxi driver already pakat wth boat operator. bringing us to motorised boat terminal & they wanted to charge us thb1500/boat..I tried bargain down to thb600 but they started to get relentless & show me the association fixed pricing & etc...at the end decided not to use their boat & asking the taxi guy to bring us bck to Bangkok!!...The taxi guy dunnop what to do & discussed further wth the boat operator & atlast they agreed to reduced to ~thb1000...That's where the interesting crowded floating market tour started....It's a must for 1st timer to BKK! For me BKK is abit too modern to my taste & I like the floating market!! 

i'll be meeting up my friends at the Suvarnabhumi airport
they're flying from vietnam to bkk
while me fly from malaysia to bkk