Those are the minimums for dualing from a Fighter to a Mage, yes. You can go higher if you like. If you were going Ranger to Cleric like ussnorway recommended, you'd want 15+ strength and 17+ wisdom.

Also, when they are talking about the PC's potential power, they are talking your god blood, it has nothing to do with your class.

You'll absolutely want to have 18 both in strength AND intelligence at level 1 anyway so don't bother about the requirements for dual classing.

You will also need a dex of at least 15 to go from Ranger to Cleric & unlike other duals you can't take a kit like Archer or Stalker if you are playing vanilla... there are mods that remove this kit issue.

Alright, so I've been looking around a bit and from what I've read the reccomend level to dual Fighter to Mage is 13 instead of 9, what are the advantages/disadvantages of this?
Also, would it be a bad/good idea to dual a Kensai into a Mage? If Mages cant wear armor anyways to cast spells, surely it wouldn't be a bad idea to get some melee damage bonuses if you aren't going to be wearing armor in the first place, right?

Also, in character creation, when I try to raise my Strength to 18, it goes from 17 to 18/16. What does this mean?

Waiting until level 13 will yield a slightly more powerful character at the XPCap of 8,000,000, which you won't reach if you play a normal party game. It's not recommended since this raises the desire to cheat or use exploits to justify your build.

If you dual at level 13 instead of 9 you'll switch to mage at 1,250,000 instead of 250,000 XP, won't get your fighter abilities back before 2,750,000 (after about 60 percent of the game) instead of 500,000 XP and will be additional 1,000,000 XP behind as mage until the end, most of the game will be over when you get the first HLA.

The benefit of waiting until level 13 instead of 9 are +4 to hit and an extra half attack per round when dualclassing is finished.

Kensais are quite popular for dualing to mage (like any exploit) because they can wear mage robes but be aware that the equipment slot for gauntlets or bracers will stay empty for the whole game and you can't use bows.

The second strength number (from 01-100, 00 is actually 100) is a bonus only warriors get, the higher the better but it's not too important.

Well alright, then I suppose I'll go with a Kensai and dual at level 9, thanks for the help.