Jim,
Your numbers work.
A few other thoughts:
The tips are seldom as effective as the main wing area, particularly if they have a 'pleasing' shape in the plan view (looking straight down on the wing.) If they are rounded or tapered down as seen from the front or rear, they also act less like the main airfoil area. Tip effectiveness drops due to "tip vortices" - spiralling air trailing off the tips. The air "below" the wing also flows out towards the tips - higher pressure seeking lower pressure. The air "above" the wing produces most of the lift by being at lower pressure, further drawing the higher pressure air from "under" the wing to wrap over the tips. ("Above" and "below" refer to the direction of lift at any given moment. Towards the "pilot's head" in upright or inside maneuvering, and away from it in inverted and outside maneuvering...)
You could choose to start with a tapered "planform." The average of the tip and root chord lengths is the average geometric chord for the wing - it's that simple.
Wing sweepback (or -forward) is another thing you can play with. Aerodynamic sweep relates to the quarter chord (25% back from the LE) of the wing. Flite Streaks and Ringmasters have slight forward sweep. The LE is straight, and the TE slants forward... A P-51 Mustang wing has just about zero sweep at the quarter chord: the LE slants back about 1/3d as much as the TE slants forward... It's just a tad more complicated to find the quarter chord for a tapered wing, but it should be close enough to find the average chord (average of tip and root chords) and 'place' its quarter chord on the line drawn from 1/4 of the root chord to 1/4 of the tip chord.
CG also relates to the Mean (average) Aerodynamic Chord, not the root chord unless the wing is rectangular, like your example. (Aerodynamic chord is not exactly the geometric average chord, except for rectangular planforms. Still, it will be close...)
And finally: there are two ways to figure the Aspect Ratio. Simplest, for rectangular planforms, is Span divided by Chord.
But if you have an elliptical or tapered wing, what then? Can you figure out the area? If so, and you know the span, you can find the Aspect Ratio.
AR = b/c (span is usually labeled 'b', maybe from 'breadth' of the wing? chord is 'c'.)
Algebra lets us multiply both sides of an equation by the same value without changing the result, right? So, let's multiply both sides of that AR equation by (b/b)...
(b/b)*AR = (b/b)*(b/c),
On the left side, b/b = 1, so it cancels out, leaving AR unchanged.
On the right side, we don't do that, instead we see that the expression (b*b) / (b*c) uses the two things we DO know: span (b) and area (b*c). (Area is often represented by 'S', from working Surface?).
So, we wind up with AR = b^2/S.
This probably doesn't do much for your initial question, but it might help you see that it isn't hard to get a bit fancier, when and as you want to.