94' Ranger 354XT, original 150 Fast strike, guidance needed

[RNTny]

Ranger 94' 354XT, 2F119L394
150 Fast strike
M# J150GLERA
S# G 03554657
1. Correct engine oil.
Purchased used, original owner used Penzoil full synthetic. Discontinued, switched
Sierra full syn., should I be running full syn., or XD50 or even XD100? Sierra doesn't. seem to be popular.
2. Correct plugs? Champion QL78YC?
3. Currently using WIX fuel/water separator. Racor Best? If so, recommend model.

Sorry if I over complicated this, known to do.
Thank you!