A set of test arrows as suggested by is a great investment for a wood arrow shooter. Formulas for figuring spine work OK and will get you close, but the variables between the shooter, bow, arrow length, point weight, etc, make the formula a swag at best. With the test arrows you will know in minutes exactly what spine you need.
With wood arrows, be careful with bareshafting. Bareshafts tend to fly sideways and can crack or break when hitting the target crooked. I recommend paper tuning. It works just as well, better for many, and your arrows will last a lot longer. I fletch my test arrows shorter than my regulars so they don't correct as quickly.