Pimp my Flyer!

• converting to fixed (16T cog, maybe switching chainset over to 1/8 - is it worth it?)
  

3/32" should be fine - but get a good quality cog, and maybe put on a new chain at the same time

• getting a Brooks saddle (not sure which one). Don't find the stock one comfy, think it's too narrow for my sit bones.
  

Brooks all the way - B17 is your standard route to nirvana

• replacing the bars and tape (Brooks to match seat?). Never use the drops! Can someone recommend alternatives?
  

You could try moustache bars if the width doesn't bother you

• getting clipless pedals and shoes (not sure which, I'm new to all this!)
  

Can't help you here - I'm running with clips

• Removing the decals - is this possible?
  

Sounds like a faff and could end up fugly - get it resprayed if it bothers you that much