Hair not growing

I am a 20 yr old Black male. my hair is 4b i think which is nappy / coarse. I been growin my hair for bout 1 year now puttin it in cornrows since it got long enough to braid. but i still got no hangtime after 1yr. I have the following questions im hoping you peeps can answer.

I get my hair braided every 3 weeks, how should i be taking care of it during those 3 weeks when its in cornrows.. Plz be detailed like wat products to use how frequently to use them  and what not to do etc. I havent been doing anything betweeen those 3 weeks but washing my hair like every 4 days in the shower with a du rag on.

When i get my braids taken out, i get my hair washed, blowdried then rebraided again. Is this bad? I heard i should leave the hair out for a couple days. Also if I should leave it out then how do i maintain it while its in the fro?

i hear about indian hemp oil castor oil all kinds of other stuff. I'm not too knowledgable on those things so what are simple products i can use t o increase my growth and healthy hair.

I hope someone can answer my questions because after 1 yr of growing this i should have some hangtime, im real frustrated like my hair aint growing.

Thanks, all help appreciated. feel free to pm me with more advice.