How to grow my hair longer

Hi ! I (19F) have thin long (for about 17 inches) 3B/3C curly hair and I want to grow them longer, if possible to my glutes. I've considered to buy the Mielle Organics Rosemary Mint Oil to grow them.

I want to know which routine do you guys will adviced me considering my hair type. I wash them one time a week and during my school time, I put gel on my hair every single day and because of that the hair on my roots are dry and really frizzy compared to the rest of my hair and I kept doing ponytails during this time because I didn't know how to style my curly hair.

I want to know some advice from you like : - how many times should I use the oil in my hair a week ? - should I use it on the roots or in the hair ? - if I put the oil in my hair, should I use gel after ? - which protective hairstyles should I do ?

I really want them to be longgggg, hydrated, healthyand thicker.

Thanks.