If it were my project, I would decide what wing span I could live with based upon the carry capacity of my car. Personally I am limited to a WSof about 54 inch max if I want to carry the plane in one piece. A major consideration at this point is what air foil to use. My personal preference is the Clark Y which developes high lift a low speeds.

Once the wing span has been established I would calculate the area of the wing. I have scratch built enough planes to know, based on my building techniques (all built up balsa), the empty air frame will weigh approximately 1 ounce for every 10 sq. inch of wing area. Thus a wing that has 400 sq inch of area will be supported by an empty airframe that weighs about 40 ounces.

Then I would add the weight of a "typical" power system (fan/motor/battery/ESC) plus receiver and servos to arrive at the total all up weight. For good EDF performance a usable rule of thumb is 150 watts per pound of AUW. So for an AUW of 56 ounces (3.5 pounds) I would plan on a system that can deliver 3.5 * 150 or 525 watts.

I like 4S lipo batteries and I aim for a 5 minute flight. Using a nominal 3.7V per cell, a 4S is 14.8V and the current required would be 525/14.8 or ~36 amps. A 5 minute flight * 35 amps is 175 amp-mins. 175/60 =2.9 amp-hour x 1000 = 2900 mAmpHr pack. I would select a 3300~3500 mAHr pack.

Next I would get the specs on decent 4S lipo packs (no el cheapo packs need apply) that have a "C" rating of 25 and get the weight. Similarily get the weight of whatever fans I plan on using such as Wemotech MF480's or WM400's, as well as the weight of the motors, actual weight of servos and receiver. These are all available from the internet.

Recalculate the AUW and redo the power calculation. I prefer 70 mm fans and the web sites of either of the two mentioned will have thrust data available. If the fan vendor doesn't have thrust figures, I'd find a different vendor.

My Twin Biz Jet (380 sq. inch wing area, 45 inch wing span) uses a pair of Wemo MF480 fans driven by HET3S motors controlled by 36 amp speed controls powered by a single 4Sx3300 TP LiPo. At full throttle the motors draw 29 amps each or 58 amps total. With a 3300 mAHr LiPo, the combined power is 840 watts. With an AUW of 60 oz (3.75 lbs) the power loading is 250 watts/lb, well above what is needed for good performance. The total static thrust developed is 52 oz. so the thrust/weight ratio is 52/60 or .87. This is not enough for true vertical performance but is good enough for 70 MPH level flight. With throttle management, 6~7 minute flights are easy.

All of the above calculations will give you a starting point. You may want to use a bigger pack to help in balancing the plane properly as there is no sense in adding lead balast.

Hope this helps.