who is the tour with? I have no info on Ko Muk but hopefully someone else can help. 4 destinations looks a lot in your timescale. Have you a weblink with the tour? ( it does look good though )

it is with intrepid tours

but i am not allowed to post the link

we are considering changing our date to september so we will take in

Days 1-2 Bangkok
Days 3-6 Khao Sok National Park
Days 7-10 Homestay/Ko Pha Ngan
Days 11-13 Ko Samui
Days 14-15 Bangkok

do you think the heat/rain will be a problem in southern thailand at that time of year ?

thanks so much for your response , the choice is overwhelming !