Well, I've never had a relationship with a dude and I'm as gay as a picnic basket. You? You've got the rest of your entire life to figure out what you are. Is there any real pressing need for you to pinpoint it, right this very second?
As for taking a huge cock on your first try, there's no reason why you shouldn't. You can take what most people know about anal sex, put that in a thimble and still have plenty of room left for your thumb. Here's basically what you need to know:
1. Pairing with an experienced top who actually knows what he's doing makes all the difference.
2. You, as the bottom, should set the pace. Don't go any faster than you can handle. Slow is fine, if not completely necessary on your first try.
3. There is no such thing as too much lube. When in doubt, go nuts.
Also, here's the requisite "No Glove? No Love," comment. But that's more of a common sense addendum than a specific answer to your question.