1. They're not supposed to suit the uniform. The idea is for them to stand out!
2. The Captain may well have been a management pilot (or other management stooge) if he wasn't wearing the tie. If it was his sector, it's also unlikely he would do the PA. It's not compulsory to either wear the tie, or do the PA, but it's strongly recommended if you want anyone to chat to over a beer or dinner.
3. The PAs have changed as of a couple of days ago. There are now 4 different PAs depending on the circumstances: domestic, delay, and international inbound/outbound.
4. It doesn't particularly matter when the pilot does the PA. He can do it at a time of his convenience or choosing so long as it doesn't interfere with safety. Just as with most other PAs. There are many personal opinions among pilots on which time is most appropriate, but I wouldn't be losing any sleep over "when" it was done.