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.
1. My network at home is embarrassingly not networked. I have all file sharing/print sharing disabled. I would like to change all of that. My computers have OSX, Windows 7, XP Pro, and a few flavours of Linux. I have a computer I would like to make make my server/firewall. What beginner-friendly OS is best for such? GUI's are nice! If I have a server doing such functions, do I set my router to Pass-through (or some such?)?
2. I tricked one of my employers into buying satellite broadband access for me. Haha! I already have cable broadband. The only place the satellite dish could be put was on my workshop, which is @ 500 feet from my house. The satellite feed goes into a modem and WIFI router. I have a workstation and a laptop in the workshop. I built a cute little dish for receiving the WIFI signals from the workshop WIFI router. The dish is installed in my attic (basically). The signal strength is solid. I just bought two modern thin clients on eBay.
In my attic I would like to have the receiver dish->router->thin client? Can I have this "attic thin client" on two networks? I want to have it on my house network so that I can control it from my main computer (mainly for transferring data). I want to have the thin client connecting to the internet through my satellite feed network.
Is this even possible?
I have been playing with Linux for about 5 years. I have tried many, many distributions. I have never tried a server-specific distro, but I am willing to give it a shot. This experimenting has really helped me learn more about networking and different OS's than anything else.
Thanks ahead of time.
P.S. Bonus question: My nearest neighbour is 1.2 miles away. Can I disable encryption on my WIFI network to gain ANY speed? It is very fast now, I was just curious.