I honestly tend to gloss over titles with words like "Entelecheia." You said you just learned this word, I've never heard of it myself - since I don't know it, I don't have any idea what this comic's about just from the title.
I think it's a good sci-fi-ish word for a title, but a bit long and outlandish for my tastes. If I were looking at a list of webcomics and only the titles were listed (such as how TWCL lists comics), this is one I would skip and not think twice.
Another thing to consider is typography. Can you make an interesting banner or logo with "Infinity Entelecheia"?
As far as spelling goes, I'd still argue that it's important from a marketing angle to have a spellable title. If someone's going to recommend the comic to a friend but they can't remember what it's called because it's too long or strange, that's bad.
Personally, I'd try to find a shorter, more familiar synonym if I could. The definition you posted has "Actuality", though I don't think "Infinity Actuality" flows well.
Infinity Realized. Infinite Actuality.
I'm terrible at naming stuff.
Are you already married to "Infinity"? If you really liked Entelecheia, could you drop Infinity? Dropping Infinity doesn't help help with the strangeness of the word, but making the title shorter may make it less intimidating. And if you had a really good advertising banner, maybe you could get away with it.
Though it's a bit late now, I'd have to say I don't really recommend buying a domain before you've decided on the name of the comic. At least they're pretty cheap so if you really change your mind, you could buy another one.