Is it easy to buy a motorbike?
* Yes
Can I easily sell it in Peru?
* No, it can't be sold outside Colombia
How strict is the police with papers?
* Very. They can take the bike if you are missing papers
What papers should I have?
* All papers you have regarding the bike
Can I easily cross borders?
* Yes.
Are there regions where I should not go?
* Yes. But I will not try to list. I do not have all information. And it is not black and white. Check recommendations about the areas you plan to visit.
Peru is not possible to predict at the moment. Things change from day to day.
You can get some idea from maps like this
PROVIAS NACIONAL - SGCV - Visor de Emergencias Viales
But.... there is a lot not shown on this map.
And you do not know how it will look tomorrow.
Even if it not is dangerous, it creates a lot of problems......
(I was there)
=
These pictures shows the police in Bogota + bikes loaded on a truck to be taken away to......
You do not want to end up in that situation...