No, no. Many of your statements are NOT correct.
First, make sure we are talking about the same setup:
me -> tor -> vpn -> destination
VPN is TUNNELED through Tor. Anyone outside the tunnel can not see what's inside.
In this situation, it doesn't matter what programs you run. Playing online games, streaming movies, inciting revolt, flash, TBB, iceweasel, xchat, whatever... To the Tor network, everything looks the same - it just looks like you sending traffic to the VPN. Your Gateway, which creates Tor circuits, also just sees one connection to your VPN. Nothing that you do in Workstation matters in terms of Stream Isolation. Only how you configure your VPN.
Stream Isolation can be applied to the VPN connection only. If no proxy is specified, then the VPN connects through the TransPort. If you isolate the VPN stream, then it can connect to another port on the Gateway. This is mostly pointless since all of your traffic will be routed through the VPN anyway. There is nothing to isolate the VPN from - meaning no identity correlation between VPN traffic and non-VPN traffic anyway. [If you use unmodified TorBrowser, then that will skip the VPN and use Tor normally.]
All of your traffic will go to your VPN over the same Tor circuit no matter what you try to do. There are no separate streams for a single connection to a VPN.
Your destination addresses will see somebody connecting from the same VPN. So you become less anonymous. Not quite pseudonymous yet because if you use a busy VPN with a shared IP, it's possible that many people are connecting to the same destinations from the same VPN.
If a persistent foe is able to track you pre and post-VPN, or the VPN gives you up, then they'll see that the connections all came from the same Tor exit node. This doesn't necessarily make you unique, but you've lost a LOT of anonymity. How many people connect to your destinations using a VPN tunneled through Tor? Probably not many.
Iceweasel, even in this case, is NOT the same as TorBrowser. It's true that neither Iceweasel nor TorBrowser will benefit from stream isolation because they both will be routed through the same VPN over the same static Tor circuit. BUT TorBrowser is designed to have the same browser fingerprint no matter how you route the connection. If you use TorBrowser, you will appear to be a random TorBrowser user to the destination. If you use Iceweasel, chances are good that you will have a UNIQUE fingerprint and immediately be pseudonymous everywhere.