Sounds like a good place to start. Generally Id say if you are dosing wort, do it at flameout.
Ive had a lot of luck making spice 'potions' (add spices to vodka for a few days minimum, strain and store) and then dose at bottling. This way you dont have fermentation scrubbing out the delicate aromas.
By dosing a small amount of finished beer, it is easy to scale up to the proper amount of potion to add to 5 gals. For example, add 1ml of potion to 2 ozs of beer, stir and taste. Too much flavor? Repeat with 0.5 mls to 4ozs. Too little? 2mls:2ozs. Volumes are subject to change.
Once you find the right ratio, its simple math from there.
And there is no reason why you cant layer the spice additions by doing them during boil/flameout/2ndry/bottling as long as you are tasting along the way.