This thread is a bit confusing, so I will make it worse!
My Peruvian partner says I will need the Rentista visa to enter/stay the country as a permanent resident. I must meet the qualifications, and abide by the restrictions of that visa (primarily, that I will have a foreign pension and NOT be employed in Peru, and spend at least a total of 184 days per year in Peru).
I would need the carnet to prove I am a legal resident (but not a citizen with all rights). It is my "DNI" as a foreign national legally residing in Peru.
So I need both when the time comes.
I have never heard of ANY restrictions on property ownership for a Rentista. It would seem illogical since, as a tourist with permission to sign contracts, I was allowed to purchase a condo.
Buying into a business or renting the condo out for profit might be a different matter since it might produce income that violates the terms of a Rentista. You would definitely want legal advice on that one.
Because my legal residency and investment in property in Peru is very important to me and my future security, I will definitely be consulting with an attorney in Lima to help me through every step of the process when the time comes. I am factoring the cost of this legal assistance into my cost of retirement. It is like insurance, it may not protect me from everything, I may not have any troubles, but it reassures me that I have probably done it properly. I want to minimize my risk.