It seems you won't be using Sunless Citadel (since you already know it well) so maybe he won't be including encounters of that difficulty level. Have you asked if he chose the 25 pt buy for a reason? Your assertion makes the assumption of knowing what the PCs will be facing which seems more problematic to me than what point buy is being used. What has your new DM said on the matter? Perhaps the collective gaming populace of EN World could better help you advise your DM if we had more information regarding what your DM has discussed. Will he be using store-bought adventures? Has he said he think the adventure path that begins with Sunless Citadel is harsh or easy or just about right? Since he is new, is he even aware of those advetures? If you return to your new DM and talk him into raising the point buy based on information from this thread and it winds up making the adventures too easy, it won't be any more fun than if they are too hard.
You might also point your DM toward the -
D&D Legacy Discussion - EN World D&D / RPG News
- where 3.5-specific D&D discussion now resides on EN World. There's probably some tips and tricks he could pick up there as well as in this forum and the plots and places forum.