First time in all 3. What do you recommend to do/eat/lodge for each?
No idea, as you haven't given us enough information. Why not do your own research on each place and see what takes your fancy.
Gee. Perhaps you could be a kind soul and provide a response to what I actually asked. YOUR recommendations. Or, also kindly, do not respond at all.
" What do you recommend to do/eat/lodge for each?"
You ask for recommendations.
When you ask for hotel help include a price range in Thai baht. Also for big cities include where in the city. You have to work up a budget and determine how much per day you can afford for hotel, food, entertainment and local transportation AFTER paying for round trip flights to Thailand.
Pull up each city forum on a laptop or other big screen computer for your research. At the top of each forum under the green bar is a choice for THINGS TO DO. Click it on. FAQs on the side can be helpful for many things like how to get from airport to hotel. Forum search for hotels in your price range can be helpful too. Even a simple Google search with your computer can be helpful.
Some other things YOU can do. Buy a printed travel guide for Thailand or check a couple out of the library. Old fashioned research that still works today. Or if research on your own is too confusing have a travel agency back home do everything for you. Stay for at least 2 weeks. Read the FAQs for how to handle money, how to use meter taxis in Bangkok and look up scams to avoid so you do not become a victim.