Since I may tell lies if I answer #1 I will try #2.

You have a couple of option to make this work. I would user a router that can run 2 ISP but even with a router that is designed to do this it gets messy.

Depends what you mean thin client. To do what you want all you really need is a dual nic pc and your favorite terminal server. You place one nic on the satellite internet and set the default gate to that. You then attach the other nic to your internal network and it will be able to see any machine on that network. You then just remote into the dual nic machine from any of your machines. You then just use some filesharing to get get to the files the dual nic machine downloaded from the internet.

There are many terminal sharing software you can even use the ones built into windows. I tend to like VNC but mostly because I have used it for so long.

On you last question encryption used to slow things down. The processors in the routers are more than fast enough today unless you start talking about lots of connections. The encryption on the PC side never has been a issue. Besides I don't think anything can be slower than internet over a satellite.