Is this plan too full for a seven-day trip to Thailand?

Hello everyone,

I'm organising my first trip to Thailand for November. I'm travelling alone, have a little budget, and am primarily interested in food, beaches, and a little nightlife.

This is my general strategy:

Day 1–3: Bangkok
Day 4–5: Chiang Mai; Day 6–7: Phuket

Enquiries:

With internal flights, is this too hurried?
Should I spend more time somewhere else and forego one city?
Are there any restaurants you simply must try?

Regards in advance!