My main character is an Aasimar Fighter 4/ Paladin X. That being said, he will only be able to get to level 26 as a Paladin, which according to the manual, means he won't get 6th level spells.

I know the manual has a lot of errors in it, and I was wondering if it was correct in this case.

It is im pretty certain but level 6 for paladin kinda sucks so its no loss

Well, it makes a difference on building my Paladin initially, because I won't assign too many points to WIS if I don't need to.

I started my currect game already, and my Aasimar Fighter 4/ Paladin has only a 12 WIS. Hopefully that will be enough with items I will find, because I would like all level-up points to go to CHA.

IMO its better to use the points into str since your really a tank and char only gives you higher saves n better prices/talking. Also you should just put your wisdom at 13 or 14 this will alow you to get all your spell levels without having to waste a wisdom item on your paladin or a item slot on 1 of these items

Well, if you finish the game at about 17th level at the normal difficulty level, I figure my Paladin level will be 13, which means my highest level spell will be 3rd level. I have already found a +1 WIS ring in the Prologue, so I'm betting that I'll find something more than this along the way.

If you start as a Fighter[4] then I dont see you getting to Paladin[20] in the normal game. At any rate give him 14Wis to start with. The paladin will get +1Wis later in the game anyway.
There is an item that gives +2Str & +2Wis but I am not sure if an LG charecter can use it.

Like Goon66 says, better put those level up stats in Str, since you wnat to be able to hit harder. Or take low Wis in the begining and use the level up stats for that.

EDIT: 12Wis +1(item) +1(quest) = 14Wis. That should be enough for the Normal game.

I was trying to avoid telling him he would get +1 wis through quests :p . Good characters cant use the item your thinkin about :( but there is a ring he'll get at the end of normal mode +2 wis and +2 char which he could use i guess. But where are you putting your stats if you cant even afford 13 wis?

BTW hes playing HoF aswell afterwards