If you get the Stygian Abyss expansion that's for new accounts you'll also get 30 days of gametime with it. If you plan on getting the Abyss+New Account, double check and make sure you buy the right Abyss package as there's an Abyss expansion without the new account and the 30 days, which is cheaper but it has no 30 days gametime. Both are the same Abyss expansion, just one has the 30 day gametime and the other doesn't, so that's why I say to double check that you're getting what you want.
Like others have said, you don't have to buy the expansions right away. If you haven't seen it yet, the
Dev Blog Video shows that they'll be adding another expansion too plus you'll get to see what other goodies they have planned, I think it's pretty exciting to know what's coming.
As for the Luna vendors, with the vendor search in game it doesn't matter as much as it used to about having a Luna vendor. Players can use the vendor search in game by clicking on their character with they're in a town, moongate, or at their homes and search for items by name or by prices. Then you can get a map to the vendor and either walk there or use the maps teleport function to get there faster, which is what most people do. If you want to gear your vendors toward new players I'd think any location near a moongate would be fine. Personally, I tend to avoid Luna unless the vendor search shows a good price on an item I need since the lag tends to be awful for me.
Ooh! Also if you've been gone from the game awhile you'll also want to check out the vet rewards. They've added things so it's not just the old vet rewards you remember. Welcome back to the game! I hope you and your friends will join up and get to enjoy UO together