250 WH/Mile (figured battery-to-wheels) might actually be a bit high of an estimate for a geo metro running at sub-freeway speeds, assuming you've got the Rolling Resistance
dialed in well.
If you have a 20 mile round trip with 200 feet of climb in either direction (400 feet for the round trip) it should be doable without any extreme measures.
I agree with the comments regarding your planned pack voltage. I assume you are trying to keep costs down. In this case, you can stay in golf-cart territory and still use at least a 72V setup (DONT go below this) and keep with cheaper controller, charger, etc. 72V will give you about 45-50mph tops. A decent 6.7" motor as sold by various EV parts suppliers should be fine but make sure to let the brushes get broken in, and expect a motor upgrade if you ever decide you want sustained freeway speed.
There's a bit of chicken and egg involved in the calculations but a pack twelve 6V golf batteries (720lbs) would give you the range with plenty of margin to do the route you plan for. You could likely get away with a smaller pack of nine 8v batteries as well but for an extra few hundred it would be worth it to get a 33% bigger pack.
The faster the discharge rating you can find, the more accurate it is going to be for estimating an EV's range. Golf cart batteries frequently give a 75-amp discharge rating (minutes at 75 amps) which is likely going to be the closest rating you are going to find. But as a basic rule of thumb, with an otherwise appropriate lead acid battery, dividing the 20-hour rated capacity in half will give you a good feel for the actual useful energy capacity in an EV application.
Cruising at 40mph on the level in a geo metro that weighs around 2500lbs I'd wager you would be using less than 150WH/mile. (my 3400lb MR2 does around 150WH/mile at that speed, as a comparison). The hill would require additional energy according to the equation E=mgh.
E is joules. One kilowatt hour is 3.6 megajoules.
M is mass (2500lbs, or about 1200kg)
g is gravitational constant (9.8m/s^2)
h is altitude change (400ft, or about 120m)
so doing the math and converting from joules to watt hours you get:
E = 1200kg * 9.8m/s^2 * 120m
E = 1.41 million joules or...
E = 0.4 kilowatt hours.
so you only need about 1/2 a kilowatt hour in extra energy to climb the hill, both ways.
so 20 miles at 150 wh/mile plus an extra 1/2 Kwh for the hill gets you 3.5 kilowatt hours used. You might want to add 20% to that number to account for start/stop, headwind, etc. as well. twelve 6v golf batteries have about 6KWH of useful capacity. nine 8V golf batteries have about 4.5Kwh of useful capacity. Both packs should do it, but you'll get more cycles out of the bigger pack due to shallower discharge cycles.