2. For what I've heard の is for possession, but I know for sure that it can be used in words, too. (きもの).
These are not the same thing. 着物（きもの）is composed with the word 物（もの), which is "thing" (http://dic.yahoo.co.jp/dsearch?p=%E3%82%82%E3%81%AE&enc=UTF-8&stype=0&dt...). This is not the same thing as the の particle getting turned into a generic noun--that happens through grammatical "shortcuts" so to speak. They are different even though they are used in apparently similar ways.
1. だ is the informal version
1. だ is the informal version of です.
This is not so simple--read the bottom of this page (and the rest while you're at it):
http://www.guidetojapanese.org/learn/grammar/polite
2. For what I've heard の is for possession, but I know for sure that it can be used in words, too. (きもの).
These are not the same thing. 着物（きもの）is composed with the word 物（もの), which is "thing" (http://dic.yahoo.co.jp/dsearch?p=%E3%82%82%E3%81%AE&enc=UTF-8&stype=0&dt...). This is not the same thing as the の particle getting turned into a generic noun--that happens through grammatical "shortcuts" so to speak. They are different even though they are used in apparently similar ways.
http://www.guidetojapanese.org/learn/grammar/nounparticles
http://www.guidetojapanese.org/learn/grammar/genericnouns (also may be useful)