1. Depending on it's mood and how many downloads are queued yes. Sometimes it works to use right click and press find more sources though.
2. Normal. Lots of reasons like someone else sharing the same file too.
3. Could be due to firewall (see 6)
4. Depends on their speed as well (e.g. they are on dial up)
5. dunno. Probably as good as any
6. Not really, but it means that you are not recieving incoming. That could be the cause of those transfer interupted.