[brucepick]

Good luck with it!! You'll get support here, for sure.

Does it have a manual transmission?? Being a committed hypermiler, I wouldn't buy any other type. Except maybe paddle shifters, but only if the guts is one of those newer computer controlled dual clutch things with no torque converter.

Can you drive it in 2WD mode? Full time 4WD will hurt your mpg. That's one main reason Subaru hasn't gotten their cars up into the higher mpgs like most Japanese cars of similar size/weight.

Grill block -
Get a ScanGauge, I think about $150. One of the available displays is a digital readout of engine coolant temp (labeled ºFWT for "water temp"). With that info you'll know if your grill block is OK. I keep that showing always. I need to vary the amount of grill block when the seasons change. It reads out in (approx) 2 degree increments so it's much better than the "cold", "medium", and "too late, you wrecked your head" indications on a regular needle gauge.

Wheels and tires -
If you don't need off road or snow/ice capability, highway tread will give you a definite improvement. I keep 2 sets of tires mounted on 2 sets of wheels because I need snow tires for winter. When you spring for the $$ for that, get LRR tires - low rolling resistance. My LRR Michelin snows roll nearly as smoothly as my summer tires.

Higher overall rim + tire weight hurts you in city driving due to the energy costs of acceleration/deceleration. The rotating weight doesn't hurt you so much on the highway; once you get that wheel + tire spinning it tends to stay spinning.

Narrower tread is better than wider (sorry, doesn't look better but it rolls better). Taller overall diameter will give you an advantage at highway speeds, if they will fit in your wheel wells. Less rpms for the same road speed. But your speedometer won't know you have taller tires so you have to make the corrections by doing math. There are tire size calculators to help with that.

Lowering -
I'm not sure. If nobody answers here, go to the "Aerodynamics" subforum. Probably already answered there. But see my next section on mods; the belly pan is easier to work on if the car isn't low to the ground like my Civic.

Aero Mods - should help at any speed above 30 mph or so.

If you don't need it, sell the roof rack back to the dealer or just take it off.

Belly pan is something I'd suggest. Cleans up the air flow underneath, and is stealthy. My brother has a Wrangler Unlimited (4-door) and it looks like you could easily get underneath and mount thin Lauan plywood on some angle brackets to cover the whole underbelly. Prime the Lauan first and it will be fine. Or use Coroplast (google it; buy it at sign shops) with some aluminum bar stock stiffeners added using pop rivets.