Noobie Sizing and parts specs

Hey,

I'm looking at building a KHS DJ 200 frame and had a few questions. Let me preface this with some info. I've been riding XC and light AM for a while now but need to work on bike handling skills, so DJ and urban it is. I'm 6'1" or so and I tip the scales at 230.

My primary questions are on stem/bar length. I'll be ordering the KHS in a medium (b/c they don't have a large and It's really cheap) with a 21.7" TopTube.

I'm thinking 31.8" clamp, 27" bar with 30 cm rise but I'm not sure on stem length. I know that too long of a stem will have a negative impact on bike handling but I don't want to be knee knocking all the time. 40, 60?? I was looking at either a Truvativ Hussefelt, Easton Vice or Easton Havoc stem.

Tires:
I have a brand new WTB prowler 26x2.3 just laying around but need to get another tire. Should I go something like the small block 8's or another tire like the WTB? Or just get 2 Small Blocks or something like it.

Thats all for now, sorry for the long post and Thanks for reading!

Winky