A Gentle Lady or Olympic 99 or similar is a great way to get started. In contrast the Saggita is a horror to put together with it's laminated trailing edges, diagonals and fancy fuselage shaping. You're wise to not chew off something too fancy as a first project.

Getting back to the wood quantity issue I'd suggest that you don't really want to buy only JUSTenough. Get enough extra, perhaps 50% over, that you can choose the sheets to match the task of the part. Balsa is not all created equally and it's good to have a few extra sheets to allow you to match the density, grain and flex to the application of the parts. For example take fuselage sides, it's good to have a pair of sheets that flex equally to help ensure the sides will curve in with equal force and shape. Matching the weight and then letting the sheets hang out over the edge of your bench to compare the droop is a good way to match them. It's not that the rest of the wood is "bad", it's just that it may not be suitable for the specific parts at that time so it gets used on the next project.