Welcome to the world of singlespeed and fixed gear. First, regarding the issue of brakes, I'd recommend that you start out with both front and rear caliper brakes, even if you set your bike up as fixed. Practice slowing down gradually by back pedalling on the fixed gear, and use the front brake only as needed. Regarding downhills, you can exert backpressure to control speed at a low cadence, but once you get past 120 rpm it is difficult to do so w/o bouncing on the bike. What you can do is pedal forward downhill until your cadence gets beyond a comfortable and smooth point, and then ride the front brake sufficiently to maintain that speed. Over time you will be able to increase your cadence and ride faster. I can maintain over 160 rpm comfortably for extended periods. Also, I'd advise using a clipless pedal system if you are not already doing so, but regardless you want some form of foot retention when riding fixed.

As to your bike choices, I'd recommend either the Timeline or Clockwork, as the both include front brakes, which the Hour does not. The Timeline has room for large tires and fenders, and is more practical. Both bikes are supplied with freewheels only, but have flip / flop hubs so you can mount a fixed cog and lockring. I would recommend getting an 18T or 19T cog to start out, and replacing the stock 16T freewheel with an 18T.