You're moving to my area, I know you'll like it. I'd recommend doing a little research online and taking some day trips, there's so much cool stuff around here within an hour's drive or so. And if you're into history, there's a ton of it here.
My family's been here since the 1700's (even earlier on the Bay), so I wouldn't know personally, but I've never seen or heard of anyone being unwelcoming to a newcomer. People are pretty friendly, I don't think you'll have any difficulty.
Don't know about alternatives to Comcast, as that's what I've had for a long time. I think there's Fios in certain areas and a satellite service. (Be advised, there's no cell service at all on any carrier in the areas near Camp David and some other areas in the MD and WV mountains.)
We're equidistant from Baltimore and D.C., which is kinda fun. We get local tv stations from both cities. There's Amtrak train service to D.C. Not to Baltimore though.
Here's the County site:
http://frederickcountymd.gov/
And the City site:
http://www.cityoffrederick.com/
Wiki:
https://en.wikipedia.org/wiki/Frederick,_Maryland
p.s. Don't forget to register to vote. And welcome! 
p.p.s. If you have to go to work during rush hour down I-270, get to know the back roads. It's awful.
Oh and, if you have more questions once you get here, you can pm me.
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