I’d be very careful about trying a fixed gear. I thought I’d have a go on one about a year ago (with a front brake) and now that’s all I ride. Every morning I have to go into the garage and feel bad about the unused DeRosa, Tommasini and Colnago hanging there gathering dust. Occasionally I take one for a ride but the freewheel now feels weird and the riding kind of boring. The fixed gears have vastly improved my fitness, so much fun. Most days I commute 48-14 as that’s what bike came with. Mostly smooth commute with some small gentle hills. I now have other bikes with different gearings so never have to change cogs or flip hubs. Don’t ride fixed as hard to go back.