As per my handbook specs, Triumph recommend Mobil 1 - 15W40, synthetic or semi synthetic oils, API SH or above. Oil changes are every 10,00km's or yearly. I called Triumph as the dealers here do not even use this oil, and they agreed it didn't matter, but it was more important to keep range of the grade of oil down. IE: stay away from a 5W50.
As I never drive the bike under 0 deg C and I use a garage, I chose to use Castrol Actevo 20W50, semi synthetic, year round. I change oil every 5000 kms. I use a filter from the list in interchangeability list below but normally a triumph or hi flo because they are easy to get in the area but would also consider the honda filter.
some useful links for your reference:
parts interchangeability -includes filters and oils
motorcycle filter cross reference
As for the plugs, my handbook calls for an inspectionat 20,000kms or 2 years, replacement at 40,000 kms. I replaced them at the inspection interval at 17,500kms even though they still looked OK. I was there anyways doing the valve gaps and plugs are cheap.
CM