I used 14", 16", 18" and 20" hair from Fashion Leader Hair, an aliexpress vendor I would buy from again and again! The hair I bought was body wave and in colours 4 (medium brown) and 1B (natural black). There was about 500g of hair in total and it has to be bleached to be dyed red, I used 40vol peroxide with blue dust free powder bleach, then dyed over that with Mellor and Russell Red Alert as its 99p for a box in Savers and I needed about 12 boxes to cover all the hair. To bleach and dye hair, you'll need foil to protect your surfaces, disposable gloves, mixing bowls and tinting brushes. All of this is available at your local beauty supply store, as well as discount stores like B&M, Homebargains, Poundland etc if you're in the UK, I'm sure if you're elsewhere in the world your discount stores will sell them too, and of course eBay is your friend!
I mixed the bleach and peroxide to a cake batter like consistency, saturated the hair in in, folded it in the foil for about 15 minutes. The hair being brown, and using 40 vol bleach, the hair didn't take long to process light enough to put the red on. After rinsing and leaving the hair to dry, I applied the red to the hair, then again rinsed and left to dry. I cut the wefts into approximately 10" strips to make it easier to sew in rows as well.