Guys,
Different woods need different approaches, softwood is a lighter touch then cleaning hardwood.
Sealing
This is really an american term for oiling
Sanding
Yes we do sand decking if need be, esp handrails & spindels,
you need no more then 80 grit on most decking & furniture, we use either proflie, orbital or our big "boy" sanders, DeWalt and Makita makes of choice.
Choice of stain & oil for us is Cabots as billyc stated expensive but very good, expect to pay around £50.00 per gallon inc vat & del.