What would you think would be a good machine for this task?
As mentioned earlier, what you have will probably work fine. I would suggest saving all your documents, pictures, videos, music, etc. to an external hard drive and do a fresh install of Windows.
Can any of you give me any pointers on how to limit the OS as to updates that swallow up huge amounts of data?
You can turn off automatic updates by clicking Start then All Programs then select Windows Update and click Change Settings.
Any good add blockers out there that should be used?
I use uBlock with Firefox browser.
Any good programs that I should be thinking of to play my ISO files?
I also use VLC. It's free and plays virtually everything.
Any ideas of a good USB Tuner?
The device I use is a SilconDust HDHomerun which has two tuners in it. It's not USB but connects to a computer using an RJ45 network cable directly to the computer or through a network router using a cable or WiFi. Windows Vista Home Premium includes Windows Media Center software which is excellent.