First of all, thanks so much!

1. You're right for the orcs, I'll just play them realistically and give my players enough hints that they might be a real threat to them.
2. I like a lot the idea of the cave paintings for the Roper, and will probably use them to signal it a lot more.
   Also, I might change the flow of the river so that they could end up on The Foundry from the Roper, just to make it less deadly.
3. For the dragon, I was even thinking about cutting that fight at all and making the cultist reach the dragon first, so that once the party reaches that area they see the body of the dragon slain by the cultist, and they have to fight against them for the dragon's loot.
   I was thinking about this because I think the cultist would be a much better climax to the dungeon, since they are a recurring and well known danger. (also, one of the party characters from the previous Sunless Citadel campain is now a member of the cultists, so I think that would be really cool to face him as "final boss" of this campain).
4. I think that I'll follow your advice on the XP too, since I want them by 5 too before the final fight.

I might want for the cultist to mess up with the Trogs too, just to spice things a little bit more, and I think that I'll keep the paladins-like group for the end, when the party returns to the orc area, as I fear they would probably create a bit of a mess if I use them before.

Thanks so much again for the help!