I want to create a smart bracelet, where to start?

Question

Do it yourself

1) What part to buy for a bluetooth connection (minimum price and the ability to transfer small information through the bracelet)?
2) What difficulties await me?
3) On what sites to look for the necessary information?

Answer 1

Have you already mastered blinking an LED on an arduino? Any SPI and I2C too?

Answer 2

1) Any bluetooth controller compatible with all the rest of the architecture that you did not specify
2) Depends on your experience, which you did not specify
3) In Google
If you are a beginner in electronics, take an arduino or a clone and make something based on it. And then take all sorts of AtMega and stuff.