A huge assumption.
If you're wrong about that and you get a non-tech co-founder, you're toast.
Personally, I'd hedge my bets with a second tech and worry about the non-tech stuff later.
I have been in the exact same situation twice before and here's what happened both times: I was working 100 hour weeks and my partner was bored. Then he went out and oversold what I could have delivered. A disaster. Twice. (You'd think I'd have learned.)
The problem isn't whether you have the skills for what is needed. It's whether you have the time to do it. I underestimated what it would take and didn't account for all kinds of stuff. It's a very easy trap to fall into, believe me. The stuff that bites you in the butt down the line will be technical; count on it.
I would have traded either non-technical partner for a fellow hacker in a heartbeat. If I had, who knows, you may have been reading this at Eddie News instead while I typed it from my yacht. Don't make the same mistake as me. Get another tech.