First of all, Eternal Blade can't be entered before level 10, as it requires +10 BAB.
Personally, I'd just go straight Warblade 20//Factotum 20 for elegance, or possibly mix it up with a PrC on one side, probably Eternal Blade on the Warblade side as you plan, if I was going for maximum Int synergy. A three-level Swashbuckler dip... yeah, sure. Factotum by itself gets plenty of Int synergy, though, so I wouldn't do much more than that.