Something between 260x and 460x would be nice. There will be a few nights when you can use a power between the two. Still, 260x is a very good power for average nights. With my 10-inch LX200 GPS I mostly use a Televue Radian 10mm, a wonderful eyepiece that gives me 250x. (For you, the equivalent would be the 12mm eyepiece.) I also have an 8mm Radian for 312x--a subtle difference, and I could probably live with just one of the two. The lower power would be the better if I had to choose, since I can use it on more nights. I also have a Televue Barlow that would give me 5mm, 500x. So far I don't have much occasion to use such a high power. Some day I'll probably buy the 14mm (I wish I had it instead of the 8mm), and have the ability to get 178x and 357x. That collection (178, 250, 357, and 500x) would span most observing situations well.
Eventually, after you've had a chance to borrow other people's eyepieces at star parties, you'll probably invest in some pricey eyepieces. The eyepiece, after all, is half the optical system. But you can live with Super Plossls for a good long while.
It does matter how good your Barlow is. I had never liked them; until I bought the Televue Barlow, I had owned two other less expensive brands and found them to be worthless. No longer. I like the Televue Barlow and use it at times (partly to get longer focal lengths when I do planetary photography with my digital camera). I also picked up Celestron's most expensive Barlow on a whim, and it's not bad--a step up, at least, from the cheap ones I had before.