I'm up to date on Portugal's various STR restrictions.  

If you ever have to go to court on something like this you will be in the odd position of being both the landlord and the tenant, so I would leave nothing to chance or interpretation.Personally, I agree with Nathan - I'd have real questions about any potential tenants that were OK with this kind of arrangement. 

One other thought is fully furnished mid term rentals.. these have worked very good for us in Vegas we get a double or better rent premium on ours.. much less work than STR and you dont have to worry about ordinances or HOA restricting them..

They promise 100% financing, but their lending criteria are incredibly restrictive.

ONE window that will stay up on its own in each room, no holes in flooring (oddly strict on this one, even a dime size tear in a floor is considered a tripping hazard) a light in every bedroom and enough room for a twin bed and a dresser.

These are just Marketing ploys to try and get you to sign up for a program and the odds of being successful are pretty much zero.

Bond markets had 50bp cut at 60% odds before the announcement. 

Look for an existing one that has the cashflow.No deed restricted community.

I live in Tahoe and there are multiple restrictions on STRs so if that is in the plan check the local regulations. 

Generally speaking, month to month doesn't make a lot of sense to offer, especially when "no cause evictions" are prevented or restricted.