Scratch built models are almost always done from plans. The designer specifies on the plans what thickness to use for each part. Thinner balsa can be cut out with an Xacto. Plywood can be cut out with a hand saw, but is much better cut out with a scroll saw or band saw. Thick balsa requires the same.

You should ask around to see if any flying buddies have kept copies of old model magazines. They used to have construction articles every issue. The designer often walks you through the whole process and usually includes tips and special techniques. They always included a picture of the plans so you could study the design. You could learn a tremendous amount just reading some of those. If nothing else, you'll understand how simple or difficult they can be.