Right now the party is deep in the sample dungeon in the Holmes basic book. I had been planning to open up the lower levels using In Search of the Forgotten City but I'm rethinking that now for two reasons:
1) It may level them past the Keep on the Borderlands
2) I have no attachment to it - one of the reasons for doing this was to run the apprentices through some of the classics, and it's not one. It's fine as adventures go, but it's not special.
So once they clear out this level they should have some gold and some magic and the thieves may have advanced a level. I may put in some extra gold to ensure they all make it to 2nd level (and give them the challenge of hauling a big heavy treasure out of a dungeon) but I really want to get them to the keep and get things rolling there. There was a time when I could run through each numbered encounter and tell you what the monster was, how many, and what the treasure was but that was a long time ago. I'm curious to see how it holds up so many years later.
After the keep I am assuming the party will all be level 3-4 (Those thieves level pretty fast) and the second iconic module is of course The Isle of Dread. We should have a lot of fun there too.
Assuming things go well the party should be lvl 7-8 after the Isle and I am not totally sure what I will do after that. I thought about some homebrew stuff and that's probably what I will do for a bit if they want to keep on going with B/X D&D but I would also like to introduce them to another game...
AD&D was where I spent most of my early D&D time, more then basic. One of the classic AD&D campaigns (which has the bonus of being very Greyhawk-centric too) is the Temple of Elemental Evil, followed by Against the Giants, Followed by the Drow modules, followed by Q1. Having found this article I see that the XP's work very well and I probably won't need a lot of side adventures - I really want to run them through this! I may even invite a couple of my older friends to go along with them as I don't think we ever finished a complete run of all of these modules in any edition! So yes, now I'm looking at the B/X game as a kind of training ground to get to the main Greyhawk campaign run later this year.
Now that I have a rough plan for things, some details to consider:
1) I'll need to pick up some PHB's. Fortunately they are not insanely priced even nowadays at used bookstores and on Ebay.
2) I'll have to look at houserules when we get there. Plenty of time for that.
3) When I first looked at doing this I thought about letting them bring over their characters from B/X and convert to D&D but I've been rethinking that. The B/X campaign could be picked up at any time again and it's not set in Greyhawk, so I'm not going to do this. I'm going to have everyone start new characters at 1st level and we'll go from there. If I keep it in the family, they can each have 2 characters to give us a party of 6. If some friends join in then we'll go for 1 apiece. I have plenty of other modules to bring replacement characters up to speed if we need to, so I think this will work well.
Anyway, that's the plan - the Basic characters will end up around 9th -10th lvl most likely and then will probably go on the shelf while we dig into old school AD&D to play some more classics.