Hair colour at home,what developer do I use ?

[wheneverything]

Hi
I'm thinking of colouring hair at home using L'oreal majirel
Can anyone help with how many tubes ?
And what developer ?
Would it be 20 volume ?
Also how much of each ?
Thankyou

Google: To mix L'Oréal Professionnel Majirel hair dye, you can follow these steps:

Mix 50 ml of Majirel with 75 ml of L'Oréal Professionnel Cream Oxydant
Mix in a 1:1.5 ratio
Use a 20 volume (6%) cream oxydant to darken or lighten hair up to two levels
Use a 30 volume (9%) cream oxydant to lighten hair up to three levels
Mix until the mixture has a creamy texture
Apply to dry, unwashed hair with a tint brush
Leave on for 35 minutes
Gently emulsify the mixture
Rinse hair thoroughly until water runs clear
Use a shampoo for colored hair

Developer depends if you are going e.g. to lighten colour by 2 shades...

What colour would get me a medium brown without any red in it ?

I was thinking 5.3 ?
Any ideas
I always go dark with hair dyes