you will need
A chainring your existing one may do, i use this one made by salsa as its single speed specific, the new ones made by renthal look nice but are a bit expensive.
A spacer kit, as said above lots of spacers as opposed to two big ones. this one made buy velosolo is nice, and comes in different colours.
Short chainring bolts as normal ones are to long, you could file down your existing ones but it is not really worth the hassle.
And a rear cog these ones made by on one are nice as they are wider at the base so won't damage your hub.
I would use a normal hub as it gives you the option to go back to gears, gear ratio is important and is up yo you and the terrain you ride. Think i'm running 32:14. i believe you should run the front ring where you would run your middle ring but its not that important as a good spacer get lets you fine tune your chainline.