How many grafts would I need to thicken up frontal third and fill in hairline? (photos)

You need to see a doctor for an examination for possible further hair loss. A normal hair density is about 200 hairs in a square centimeter. 

In my opinion, your desired look is hard to achieve at present. I'd estimate your density is 58-65 follicular units per square cm, granted with thinner hairs.  It's challenging to attain a thicker look with this density. Often what happens is the existing hairs are damaged or killed and one year later the patient looks the same (or worse). This is one of those 'hope for the best" but consider the possibility of little or no change. Your chances of achieving your desired improvement, in my estimate are about '50 - 50.' I agree that there are few other consistently good options to get a thicker look than moving hairs. But you'll need a team which cuts grafts thinly and uses small recipient sites. Your hair transplant surgery is perhaps more challenging than you might otherwise realize. 

From the photos, it is difficult to say. First I would perform bulk measurements of your hair to see just how much hair you lost. I don't think that if this measurement is less than 50% loss, that I would recommend a hair transplant to fill in this area because you run the risk of losing hair from a transplant. If however, you wanted to move the hairline down say up to a half an inch, then it would take about 1300 grafts to accomplish this goal with medium weight hair of 1600 grafts with fine hair. Don't rush to transplant just yet as I don't know for sure if you are balding significantly.