At least in reporting, that is, AP Style, we try to avoid using extraneous punctuation wherever we can, and I'm of a mind that "90s" rather than "90's" looks more elegant. But that's personal bias.

I would advise that you used apostrophes today only when they are needed to avoid confusion, as with "They all got A's on the test." Without the apostrophe, as porsche said, the word could be confused with "as."

As for your possessive problem, I think what you've got is technically correct, but I'm not sure. I recommend rewording in a way that avoids the problem, like saying "our house" and then clarifying with another sentence as needed.

I agree that you don't need any comma at all, and unless you're being VERY proper, you would probably omit the Ltd. afterward--that's how the AP handles company suffixes like that.