Rate my plan and give advice

Hey guys, I'm going to Thailand for the first time soon and I would like to have some feedback on our program and some personal questions (program below). Do you think the preogram is feasible? Are there places where it is better to linger (as one of my friends will be telecommuting so time management is important 😛 ) ? Or do you recommend that he take time off? I saw that there are no mandatory vaccines but is it still safe without vaccines? Thanks in advance! (All feedback is good)

• January 29 to February 2 : Krabi
• February 2 to 5 : PhiPhi
• February 5 to 10: Phuket
• February 10 to 11: Bangkok
• February 11 to 13: Ayutthaya
• February 13 to 17: Bangkok
• February 17 to 22: Chang Mai