From what I hear, it's a pretty good challenge, any perk, SPECIAL point, or skill suggestions before I enter the Sierra Madre? I hear Light Step is a godsend.
P.S. I'm level 26, plan on getting to level 28 before departing.

The highest speech check I can recall is 85 though magazines and an outfit that adds +5 to speech and +1 to charisma can be found before that check is made. But that is entirely optional but you might like to have all options available to you. A 75 in science and Lockpicking will let you open everything of value but those are few and again magazines can be found in the area. You are stripped of equipment upon entering the DLC so don't bother bringing anything. Very hards do exist but they don't contain anything necessary or have the key nearby.

Definitely get Light Step, yeah. I suggest leveling up Lockpick, Science, and Speech as soon as you can, as you won't get the fullest experience in my opinion if you don't have a high skill in all 3. If those are already high, get Energy Weapons and Repair.

Get your melee skill up to 50. Craft yourself a Clean Cosmic Knife (fairly easy to do), execute the special strike for that weapon in VATS and the Ghost People will die in one stroke 80% of the time.

Not to be negative, but there's no way I'm putting any skill points into Science, Just not my style, but I'll definitely get the Light Step perk and put up my unarmed skill for the weird Claw trap thing I'm glad I have High Energy, Guns Lockpick and Speech skills though.
*Edit: I have like 43 Melee too.