I know a lot of people who ride derailer equipped bikes through the winter and when it gets really cold and thinsg freeze solid they often get to enjoy the single speed experience.

To take that Paver from a 7 speed to a one speed you need an ss kit and a chain tensioner which you can buy, or you can use the existing rear derailer and lock it into position.

A rear derailer is also as fine a chain tensioner as one can get.

If you don't live in a frozen hell then the 7 speed should be fine.