Use a 2 micron for the on-engine Yanmar filter and a 10 for the Racor.
Why not use a 2 on the Racor? Well you could but then it will plug more quickly and you have a 2 on the engine to catch the really fine stuff.
Why not use a 30 on the Racor- puts too much load on the on-engine filter so it will plug more quickly. Also it is more expensive and difficult to change.
I'm not a Yanmar guy, but diesel fuel delivery is pretty generic, so I can offer this:
Fuel pumps are generally pretty tough items, and should never see any strain if your filtration system is up to snuff and regularly monitored/maintained.
I would get another racor to mount inline, so that your filtration is 30-10-2, and install a vacuum gauge with a drag indicator between the filters and the pump.