Everything about sew in extensions?

I'm getting sew in extensions for my birthday/ graduation

I've been reading and watching videos about extensions and how to take care of them

I heard you can keep them in for MAX 3 months and I'm only going to keep them for 2 because its the time in between my birthday and graduation

The only thing I'm confused by is the washing.

I know you use a nozzle and dilute shampoo with water and same thing goes with conditioner

Now you put that on the braids? Or what? and how do I make sure its all out without washing it like normal hair?

And I read that you put oils or leave in conditioner on them to give the braids a little moisture

Is that right or wrong? And if i use oil do i wash it out or leave the oil in because I already put coconut oil on my hair every week or other week.

I'm Mexican and have thick wavy/ curly hair (curly on bottom wavy on top) I mention this because i know the thinner hair like Caucasian hair don't hold the extensions very long

I want the length not so much thickness

If there's anything else that needs to be added please feel free to let me know