My Single-speed commuter runs 36/16 with 1.5" Schwalbe semi-slicks.
You can get a "complete" Single-speed kit with everything you need included from Charlie the Bike Monger:
I have one of their kits, and it has all the parts required, including shorter chain ring bolts to allow you to re-use your current cranks.
Your existing Crankset should be OK, but you might be best replacing the chain.
As to the tensioner, you might be lucky and hit a "magic" gear that fits your bike with the correct chain tension; if not, you'll need a tensioner.
One tip - measure the chain length and remove excess links on the bike, without fitting the tensioner and get it as tight as you can - then fit your tensioner (i.e. don't fit the tensioner first).
Off-Road: 1999 Marin East Peak / 1995 Carrera Furnace / 2001 Gary Fisher Supercaliber
On-Road: 2009 Univega Via Laser