The "5.1 vs 4.3" question gets asked a lot. Here's one of the threads with answers for this exact question:
Regarding which upgrades to do, that's totally dependent on which performance and aesthetic characteristics you are after, and how you rank them in terms of importance.
Performance characteristics include items such as:
- Durability (reliability)
- Gas consumption
- Cycling speed
- Shot-to-shot consistency (velocity and groupings)
- Reloading speed
As for your question about CAPS, no, there is no west coast chapter at this time.
Presently, there is only one functioning CAPS chapter, located in Toronto.
There are talks at this time to get another chapter started up in Montreal.
I know there are practical shooting groups in the Vancouver area and other west coast cities, but they are not under the CAPS umbrella. Some of these groups have been in operation for years, and even run by IPSC black badge holders, but these groups are not active on ASC. You will need to do your own research to try and find these groups (even I can't remember the names to point you to.)