the more work you have to do (if you lack experience) the more stressful it will become evidently.

If you have to paint some walls, it will be less stressful than planning a building and erecting it obviously.

Also, think about whether you are fluent enough in the langage to talk to planning officers etc. in Portugal (i don't know the procedures there)

But whatver you decide on doing.
Good luck! and best wishes! x