Wow. Congratulations. I suggest you put it next to the washing machine and dryer to *really* confuse people.
So you've got another major expense coming up to use it- do you have a mixing board, already? You'll want at least a 24 channel mixing board, and I'd suggest getting a larger one if you can- you'd be surprised how often a few extra channels comes in handy. How about monitors- or at least a stereo- to listen to? Plus all the cables to go back and forth between the ATR-80 and the mixer. Sorry if these are really simple answers, I'm just not sure what your level of experience is.
Does the machine come with a manual? If not, you may want to spend some time & money and see if you can find one. As simple and intuitive as analog is, the machine itself has LOTS of adjustments, features, and requirements that might not be obvious. Sure, you can plug it in and go and do OK for a while, but a manual will help you get the most out of your new baby while keeping it in good shape.
How about a cleaning and demagnitizing kit? The tape heads and path needs *regular* cleaning or they'll degrade pretty fast. Have to degauss them every so often, too. I just picked up one of these kits from an Ebay store:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3763012085&rd=1&sspagename=STRK:MEWA:IT&rd=1
That'll give you what you need to get started- I'm assuming since you mentioned mics that you already have some. A role or 2 of tape, too- think that's a 30 ips (inch per second) machine so a standard role of 2500 feet is going to give you a bit less than 17 minutes of recording.
There's more- much more- but I'm not sure what your experience is and don't want to talk too much over or under you. Let us know how what I just wrote hits you and we'll talk more when I have a better feel for what needs to come next.
That's pretty exciting. I was just oogling one of those machies on Ebay and wondering if there are going to be any left by the time I can afford one.
Take care,
Chris