John,
I'd install the oil tank before you mount the motor! And you might consider installing it further forward, just aft of the fuel tank; the fuel tank support extends back maybe 4-5" aft of the tank, so you could just extend that a bit. I've been using PVC board lately for that sort of stuff . . . it's not real strong but easy to work with, and unlike starboard, you can glue it with PVC cement, and no worries about rot! If you mount oil tank with the fill opening on the aft side, so it's under the hatch, you might be able to fill it w/o using a funnel & hose!
The barbed fitting is actually on the outlet side of filter; it's real handy if I want to drain fuel out of the tank! (The boat is my reserve fuel supply for vehicles during hurricane season! In the past, power has been out for a week after a storm, and gas stations weren't able to pump gas. They are now required to have generators, but it's also handy to be able to drain a nearly empty tank and then refill it from 5 gal. jugs to re-calibrate gas gauge & I-Command fuel management gauge.) I have a long hose that's open on one end with an OMC fuel line connector and primer bulb on the other end. If I want to drain fuel, I just run the hose out thru the hull drain hole into a gas can, plug in the connector and squeeze the primer bulb to start the siphon.
I also have a 3-way selector valve (with red handle, at front of splashwell) upstream of the filter with one of those barbed fittings attached, so I can shut off fuel or draw from main tank or auxiliary tanks. For Bahamas runs, I had three 6 gal. OMC tanks rigged up in series that I would plug in to that fitting. On 2 of the tanks, I drilled out the rivet in the gas cap and replaced it with a brass barbed elbow fitting to which I attached a short length of hose with a plastic fuel connector on the other end. Those tanks have 2 pins near the fuel fitting; one pin opens a fuel valve and the other opens an air vent. For the first two tanks I drilled a hole in the plastic female connector where the air vent pin is, but left the connector to the last tank in line unmodified. Since only the last tank in line was vented, the resulting vacuum in the other tanks would pull fuel from the last tank in line until it was empty, and then from the next tank in line, etc. The system worked well and allowed me to run over two hours before switching to the main tank! Not sure I would use this system with the E-TEC because it was set up for my old 1975 vintage motor with 5/16 instead of the currently required 3/8" fuel lines. All the new "clean tech" motors are set up to run fairly lean, so they're much more sensitive to air leaks and fuel restriction. They might not tolerate potential air leaks and restrictions from all those connectors that an old carb'd 2-stroke wouldn't even blink at!
Regarding your Fuel Filter, instead of buying the Racor filter with the steel filter head that rusts, I'd recommend using what I switched to: Get a
Sierra filter with SS filter head. Keep the filter canister for a spare, and then get a
Racor B3201 assembly with includes S3213 Merc style filter element and plastic bowl, and install it on the SS Sierra filter head. The pics I posted show my old setup; I'll try to take a pic of new setup where I switched to the SS filter head, eliminated a bunch of restrictive 90 degree elbows and installed a
Racor RK11-1676E vacuum gage with a tell-tale needle to monitor highest vacuum it's seen, which tells me when filter element needs changing, in addition to monitoring the overall level of fuel restriction between tank and engine. (BRP limit is 5" Hg.)