Should I enable or disable the firewall if I'm using an external router?
Should I leave the firwall enabled or disable it if I have wifi off and only using an external router with a firewall? Generally, I would disable it if I'm using the another modem device like a DSL with an external firewall to avoid double NAT. But, since there is no bridge mode and the router is basically always in play on the ht2000w, should I just leave it enabled? Plus as I understand the ht2000w is always translating ipv4 addresses because the Hughes side of the gateway is only ipv6. What are your thoughts and or advice?
For all intents and purposes you're behind a double-NAT on satellite.
Unless you have hackers in your house using your local LAN, I wouldn't worry about the firewall much. Think they just included it because it was part of the router firmware.
Think you're safe leaving it disabled, unless you want to use the parental features, etc. underneath it.