My very first question would be, is Binder 20 focusing on versatility viable, or is it better to focus on one role?
I'd say go for versatility, especially if you're not going to take KotSS.
Binders seem to have a lot of options if one knows how to tweak them, might aswell take advantage of it.
Speaking of KotSS, it's a great PrC, but I'm not one of the ones that thinks taking it is mandatory.
Only really good reason is if you find any "fiver" ability that you want to use more often, or that your final BAB score will be 16 (epic for one thing).
As far as the point buy is concerned, a good general-purpose one seems to be (assuming Human as a good default race), with 32, 14/14/14/12/8/16. With a 38, we can neatly make that 16 Cha an 18. Would the six extra points be better invested elsewhere, say, making Con a 16 and Int a 14?
Definitly Con/Int raise.
Cha 18 is only better if you have a specific goal in mind that will include Save DC's.
Going for versatility, more HP and skills are preferable.
As far as Feats go, I'd pick a few good general ones, much as the handbook suggests.
Improved Initative is good on any character, Power Attack is good on any melee one etc.
If you eventually find out what you'll be doing, then a few more specialized feats are in order, like [X Archery-Feat] or [Y Charging-Feat], or perhaps [Z Badass-Feat].
Specialization is only good if you have a clear goal in mind, otherwise constructing towards versatility is better.
Options are, as we all know, a good thing.
I've never played a Binder, but Ignore Special Requirements seems pretty useful.
Not only can you bind vestiges that hate eachother, but you won't have to be in the Abyss for contacting Astaroth (Disclaimer: I know there's one vestige that can only be contacted on the "X"th level Somewhere. I don't know if it's Astaroth, nor if it's the Abyss. But there is someone.) nor do you have to have a body of water near to bind whoever requires that.
Given the choice of Expel Vestige and Ignore Special Requirements, I'd go for the former sooner.
You might be able to wait for ISR for you're 11th level bonus feat, but I'd take it into consideration sooner.
Then you can take Expel Vestige at 11th and you're pretty much set for all Binder-needed feats.
As far as equipment goes, Veil of Allure (Sandstorm/MiC) is really good, Circlet of Persuasion will help you a lot and you already mentioned the expensive Phylactery.
Otherwise, there's the good 'ol standard gear in +1
Something Weapons, +saves items, belt of battle, +1
Warning Eager gauntlet, extradimensional storage utilities, scrolls, potions, wands, caltrops, rope, marbles, lard, 11+ foot poles etc.
Picking Vestiges:
I'd say that you write down a quick summary of the different abilities the vestiges have on pieces of paper, then mix them up and draw two at random. Ponder what you could do with those two, write anything that seems good down and repeat.
That's how I figure out new card-combos in CCG's and it should work here.
The vestige-combo section of the handbook helps, I'd advice you to take second look through it.
Formating sucks, but the advice is still valid