I've been playing for 3 generations in a row with a shielder holding a Sarranid Cavalry Sword and being 21/15 or 18/18. For me 18/18 works better cause of the extra shield point you'll put. A shaska, like a SCS, is not a fast weapon and you'll be receiving lots of hits on your shield, and as you are wielding a knighly kite shield (not that tough), you'll need that extra resistance. Also it will allow you to use the steel shield from time to time, and you'll want to use that instead of the huscarl's because steel shield is 1 slot and will leave 2 free slots to wield an anti-cavalry polearm or even a crossbow.
Also, in playstyle, rely on your weapons reach. Most of the 2 handers/polearmers tend to understimate your weapon's lenght when they see you're a 1h. The shaska has good reach and you'll sometimes surprise guys in the approach strike if you master it correcly (works best with right strike). Also don't hesitate on backpeddaling while swinging when you're facing a fast 1h (steel pick or warhammer users), so you outreach them.