I would make the tea / try the tea & see how strong the flavor is... Do bench trials, of a sort..... So-many-ounces to 1-cup, then up it a bit with another 1-cup measurement of water..
If you find a flavor you like that way, you could adjust the amount of water for however much of the spruce you have.. Then brew most of the tips in a fraction of the full volume, to make a concentrate & thin it out in your primary... You could probably even add the tips in a straining bag to the primary if you wanted more flavor..
You're gonna want to measure & add some form of acidity, and something for body so it doesnt turn out 'flat' - golden raisins, bananas, honey maybe.. Wouldnt take the SG above 1.085.. If you use honey, it only takes about 2/3 the amount of honey as it would sugar (recipe calls for 9lbs of sugar, you'd only need 6lbs of honey, roughly) - but its always smart to add half of your sugar source, re-measure, and adjust again so you dont overshoot it..
This is all just 'winging-it' but i think you could dial it in pretty close & then get even closer on a 2nd batch