I've always used NGK plugs. Never had an issue with them.
Regards oil, any marine-grade TC-W3 compatible oil will do, but you can't go wrong with Yamlube or Quicksilver. The stuff you've already mixed up - use for a bonfire or in your lawnmower. Pretty sure there's a fuel-bowl on the outboard side, check and clean this too while you're at it.
Is that with or without VAT?