Hey guys so I'm 20 from Australia male and planning to go solo to thailand for 2-3 weeks hopefully around October (I plan to spend my birthday there)

I've been reading up on Reddit about other people's itinerarys and plans, and in the mean time been trying to rough together some sort of a plan. Let's just say it's not going great.

I'm considering just booking a flight to and from bankok and sending it, just planning as I go. Is this a good idea being it's my first time solo travelling.

If you guys can take the time of day to give me a rough itinerary that would get the most partying, exploring and relaxing out of 3 weeks that would be awesome.

Should I visit multiple places like Chiang mai Pattaya etc or just stay inside the one place and explore?

How does travel ( trains busses) go in thailand? Should I rent a car or scooter?

Again I really have no idea where to start, if I should book hotels in advance. Should I book tours in advance, flights inside of Thailand in advance? Or can I just walk around googling things to do and take it from there, booking hotels last minute

Any travel advice, locations would be awesomeee