>For stretch marks, getting the single liner 1.5mm roller is just as good as the single
>needles?
The single needles are the most effective. A one liner is very effective.
>Between derma-rolling, with a frequency of 3 to 4 weeks, do I use the single liner roller
>just once on each scar, covering few scars each time?
Yes. Roll each stretch mark very densely. "Crush" the scar collagen.
> Is it necessary to have bleeding during this process as it is expected that the needles be >pierced in deeper than the normal roller?
It depends where you roll and how thick your skin is.
The thickness of the skin is not the same all over the body and it differs individually as well. It is not necessary to get bleeding.
>Could I use a mixture of cocoa&shea butter, Vitamin E oil, argan oil, castor oil, virgin
>olive oil, rosehip oil and skin evener after rolling and also on a daily basis on the scars?
Yes.
>Could I also add lemon juice and fresh aloe vera to this mixture? Or do you suggest me
>applying tretinoin and infadolan instead.
I am not sure why you want to add lemon juice because it contains only a very small amount of vit. C. Aloe vera is a strong anti-inflammatory. You can apply it but not right after dermarolling, If you roll in the evening, you can apply it in the morning.
In my posting #4 I link to the studies explaining why to use Tretinoin. It depends on you.