i would try 42:16 or 46:16, i have used these ratios on two different converted bikes for road use, and with slick tyres like those suggested in the post, the bike will be more than capable of covering short distance commutes, i would not put more money into this project as necesary as it is no match for a road frame and my first foray into single speed i spent much more money than necessary but it was more of a learning experience, i used a converted ss mountainbike with slicks 26" x1.5 at uni in york its f-ing bomb proof (46:14)
i would try 42:16 or 46:16, i have used these ratios on two different converted bikes for road use, and with slick tyres like those suggested in the post, the bike will be more than capable of covering short distance commutes, i would not put more money into this project as necesary as it is no match for a road frame and my first foray into single speed i spent much more money than necessary but it was more of a learning experience, i used a converted ss mountainbike with slicks 26" x1.5 at uni in york its f-ing bomb proof (46:14)