I commend you on your optimism. Without positive thinking not much would get accomplished in this world. I would like to offer a different approach however. The joy in setting up a layout, whether it be indoors or out, cannot be overstated. That wonderful feeling can be dampened when play time is over. I believe i am a bit older than you and have been around the block a few times.
Personally, I would find it a chore to have to dismantle my layout each time I was finished playing. With "O" gauge track it can be a real PITA, both setting up and dismantling over and over.
May I suggest "G" scale. Of course I do not have any clue as to your financial position. But a "G" scale garden railway can be built for less than you think. And if the cost of brass track frightens you, consider plastic track. All of the "G" scale brass track made, by any of the manufacturers is UV resistant. Most of the plastic track is also, but you would have to verify that with each brand.
Plastic track you say ? How will my trains get their power ? I converted to battery power seven years ago. There are inexpensive ways along with more costly ways of powering your train using batteries. Battery power is too broad a topic to cover here. But that does not mean it is complicated.
The bottom line on "G" scale trains is that LGB "G" scale trains will operate in the rain. I don't know about USA Trains or Aristocraft. Bachmann large scale will not fare well in the rain. So your layout can remain outdoors permanently. My garden railway will be over twenty-five years old this year. Some of the rolling stock lives outdoors. the locomotives are either put away or covered at night.