1 & 2: You can ask for a match, but AA is unlikely to match CO, particulary at only the silver level. Sometimes they will match a level lower and enroll you in a challenge. In your case, they will probably not match and will suggest you take a challenge.
3. Virtually all fares are upgradeable. Industry discount, consolidator and bulk fares are not.
4. Generally, no. Take a look at AA's awards on aa.com to see all of the possible awards.
5. You will not get AA miles for any BA flights across the atlantic. This includes all flights from the americas to europe, not just flights from the US.
7. It depends on what makes an airline a good choice for your. From MIA and ORD, AA has many flight options.
8. Yes, I think so.
9. It depends on the flight and when you upgrade. If you plan very early, you may get upgraded, otherwise you may have to waitlist.
10. OW is not as strong as star, but one nice thing is that you get elite bonus miles on all qualifying oneworld flights.