Hi Trisk!
How exciting that you are retiring to Portugal. Let me preface this by saying that I am not a mountain biker, but I did spend a few years trying to be one, and gave it up when I realized I was not willing to practice enough to get good, because it took up my road time and miles. I had a full suspension bike (a 2005 Norco, regular 26er) that did make it easier to roll over roots and rocks. Now, I never got the point where I was good at doing it going uphill, but it gave me a lot more confidence. So part of me says, it might make it a bit easier for you, as well as be softer on the joints. Others will dispute this, and say it's not necessary. I rode a few dirt roads in Maine a few years ago, and I appreciated the FS even then, because it was full of huge rocks.
I have a mountain derailleur on the rear of my custom road bike, with an 11-34 and a 50/34 on the front. I can get up anything with it. I can't remember the exact gearing I had on the Norco, but it wasn't quite as low as you are talking about. I'd say, go for the lowest gearing you can get, because my favorite saying is "your most important gear is the lowest one."
I think this applies to mountain biking, too. You want to have fun and to be able to use the bike for shopping, etc. Why make something that is technically difficult harder? I never felt my full suspension mtg was super heavy, because you can't compare it to a road bike.
Where in Portugal are you moving? I am going on a cycling trip in about 5 weeks; we will be riding from Lisbon to the border of Spain.