You need to apply for Thailand pass yes.
(Lots of info on group this last week how to do that)
Insurance you get from an insurance company and its
*****
dollars now.
(One of the most asked questions here on group again search button)
Hotels there will be a choice of a few hundred to suit different budgets, remember costs include transport from airport and 1 PCR test.
No idea what time you plan to arrive or what time your flight is to Krabi. As its all only starting monday nobody knows how long all the process will take.
When i recently did sandbox in Phuket it took 6 hours from test till i was allowed to leave hotel.