Hi m8, 
  
Silkolene Pro-S 5w 40 / Sump capacity 4.7 Litres - Available from Oilman Trader 
  
Tyres - Both good brands, although softer compounds, might unsettle the Zed, but generally very good in the wet! 
Those tyre sizes you mention are OEM, and are fine. 
  
P2 price - expect to pay anything from £180 - £300, less if you supply Oil, filters etc 
  
Spark Plugs - Personally, I would change them being the new owner, Denso or NGK Iridium are the ones to go for, again PM oilman, he`ll sort you out a good price!