January will be my 1st time in Thailand, trip with my best mate. I don't know much about it, and need some suggestions

Hi everyone. I will be travelling with my mate from 9th to the 25th of January. I am incredibly excited and I have had a look online for a while now about places, but I get many mixed opinions, so I thought I'd ask the community. Would be good to get some ideas from people who have visited before.

We'll land in Bangkok and depart again from Bangkok, so I was thinking it would be a good idea to do some sort of "circle-back" trip. However I also don't want to spend most of the time on a bus/train/flight going to many different places. I would like to plan the itinerary as much as possible, so here's what I'd like to know:

1. If you had only 2 weeks, what places are worth visiting (we like chaotic city night life vibes as much as stunning natural places)?

2. Some places with incredible beaches (if surfing-friendly it's a plus)?

3. Is it an absolute necessity to visit the islands, or staying mainland will suffice?

4. Is there anything happening you are aware of during that time that is worth doing (festivals, celebrations etc...)?

Thank you so much in advance for your input