Nuts are kinda hard to get flavor and aroma to infuse into the beer.
You can get much more character from nuts if they are blended into a slurry then added late fermentation.
Use a blender with boiling hot water (to pastureize). Use enough water so the slurry pours easily. Let cool to fermentation temp so you don't kill yeast when adding to fermentor.
Overall, that seems like a solid plan. A pound of pecans seems reasonable enough and if you end up with excess extract you can always save it for a later batch or anything else that could use some pecan flavor.
In terms of determining an appropriate amount to add to your beer, the best method is probably to measure out small quantities and try small mixes ...