Hello and welcome.
1. Mostly false. It might be wise to watch the humidity, particularly if you live in a very dry place (Arizona, or upper Midwest winters, for example). See this article:https://www.pianobuyer.com/article/gray-market-pianos-and-cracked-soundboards/
2. Also false. These pianos vary in condition and use, and can be bought by the dealers at a variety of price points, conditions, and ages. They definitely don’t last forever, and the extent of refurbishment is heavier on the cosmetic side of things, and lighter on the mechanicals (i.e. cleaning, adjusting, reworking original parts instead of replacing, whenever possible). If these pianos have issues, they’re usually not apparent to the naked eye. This is why a pre-purchase independent tech inspection is so essential.
3. First part: sometimes true. Second part: True, if you’re patient and then act fast. Pianos don’t magically die at a certain age, but I’ve seen institutional and climatic environments that will wipe out a piano that fast (or faster, i.e. a conservatory practice room). The touch and tone gradually degrade (more so if you don’t maintain the regulation and voicing occasionally), treatable mechanical problems start to occur, and eventually the issues become serious enough that repairing or rebuilding the piano exceeds its market value.
The idea of buying a 5-10 year old used piano is a great one in theory, but there aren’t a ton of quality acoustic pianos from this age range for sale. When they pop up for sale, they tend to sell quickly. You might be able to snag a 10 year old used U1 near that amount, but depending on where you live, you may be waiting a while until one becomes available. I troll Pianomart, Craigslist, dealer websites who update inventory, but also call local technicians and let them know, local music teachers organizations (maybe they know a student who has upgraded to a grand piano, or quit, or non-playing parents who are now empty nesters). It also helps if you cast a wider net than just one brand.
Do not buy one of these pianos sight-unseen. Or any piano, for that matter. Videos are helpful, but do not tell the complete story.