Gold Box D&D - Any advice for making a party to go from Pool of Radiance to Pools of Darkness?

So I've been thinking about getting back into the Gold Box D&D games lately, specifically the Pool of Radiance/Curse of the Azure Bonds/Secret of the Silver Blades/Pools of Darkness series. I've played Pool of Radiance quite a bit, but I haven't beaten it yet. I'd like to take the same party of six characters through all four games, without replacing any along the way. Anyone have any experience with these games? If any readers want to share some advice on how to avoid screwing up this idea from the beginning, I'd really appreciate it.

If it helps, the Gold Box games use AD&D 1E rules, more or less.

By the way, I'm probably just going to avoid Hillsfar altogether.

EDIT: Here's something I wrote over on Google+:
"Unfortunately, there were a few self-restrictions I did want to abide by if possible (and if it's not TOO foolish to do so), which I forgot to mention in my blog post because I had a brain fart. I was hoping to have one person in the group be a race other than human, although I don't really need more than that. I also wanted all of the classes (the six in these games, that is) represented in the party in one way or another, and I was hoping that no two characters would be EXACTLY the same, class-wise, although it's fine if they're close. Other than that, I think I'd be up for about anything, but those are arguably already some major restrictions on my choices. I'm fine with giving the characters all 18s in their abilities, at least, since from what I hear about the hardest fights in the later games it's either that or reload a lot. :P"

 EDIT #2: After some helpful feedback from ckdecember gaming on Google+, I've decided that it might be a good idea to wait until Level 16 or 17 before switching my dual-classed characters to their second classes.

Option #1:

1. CG Elf Fighter/Magic-User (Ditch after Secret of the Silver Blades)
2. CG Human Ranger 15 ---> Magic-User (Add in Pools of Darkness, Dual-Class almost immediately)
3. NG Human Thief 9 ---> Ranger (Dual-Class at the beginning of Curse of the Azure Bonds)
4. LG Human Cleric 9 ---> Paladin (Dual-Class at the beginning of Curse of the Azure Bonds)
5. LG Human Fighter 13 ---> Cleric (Dual-Class during Secret of the Silver Blades)
6. CG Human Cleric 17 ---> Magic-User (Dual-Class shortly into Pools of Darkness)
7. CG Human Magic-User (not dual-class)

By Pools of Darkness, I'd have a Magic-User (part Ranger), a Ranger (part Thief), a Paladin (part Cleric), a Cleric (part Fighter), a second Magic-User (part Cleric), and a third (pure) Magic-User.

BUT...Can a Thief dual-class into a Ranger, and can a Cleric dual-class into a Paladin? If not, I'll go with Option #2:

1. CG Elf Fighter/Magic-User (Ditch after Secret of the Silver Blades)
2. CG Human Ranger 15 ---> Magic-User (Add in Pools of Darkness, Dual-Class almost immediately)*
3. NG Dwarf Fighter/Thief (Ditch after Pool of Radiance)
4. NG Human Ranger (Add in Curse of the Azure Bonds)*
5. LG Half-Elf Fighter/Cleric (Ditch after Pool of Radiance)
6. LG Human Paladin (Add in Curse of the Azure Bonds)
7. LG Human Fighter 13 ---> Cleric (Dual-Class during Secret of the Silver Blades)
8. CG Human Cleric 17 ---> Magic-User (Dual-Class shortly into Pools of Darkness)
9. CG Human Magic-User (not dual-class)

By Pools of Darkness, I'd have a Magic-User (part Ranger), a Ranger, a Paladin, a Cleric (part Fighter), a second Magic-User (part Cleric), and a third (pure) Magic-User.
(The only glaring problem is that I wouldn't have a Thief after Pool of Radiance, but I don't think that class is actually very important in the Gold Box games.)

*Alternatively, Character #2 could start as a Magic-User and immediately Dual-Class into a Ranger. Then, I could Dual-Class Character #4 into a Magic-User (at Ranger Level 15) immediately at the start of Pools of Darkness. That way, I'd have a Magic-User (Ranger 15) and a Ranger (Magic-User 14), plus two other Magic-Users, for a total of 4 party members who can sling fireballs.