a. Whatever seems right to you.
b. It may change slightly from coffee to coffee and according to freshness and varietal.
c. What the Specialty Coffee Association of America (SCAA) has to say:
A cup is defined as 6 ounces of water before brewing. This will produce 5.33 ounces of brewed coffee. Or 125 ml & 110 ml for Euro style coffee makers
The SCAA defines 10 grams or .36 oz per cup as the proper measure for brewed coffee if using the American standards. If using Euro standards the measure is 7 grams per 125 ml.
To further confuse things I will add a few more measures:
3.75 oz per 1/2 gallon
55 grams per liter
2.25 gallons per 1 lb.
If you want to know more check the SCAA's web page at www.scaa.org.
d. The easy answer for most home coffee brewing is 2 Tbs. per 6 oz of water. A standard coffee measure should be 2 Tbs (1/8 cup) . Be warned some coffee measures deviate from the 2 Tbs. standard. Some are even as small as 1 Tbs.
It needs to be pointed out that some coffee pot manufacturers deviate from the 6 oz per cup standard. You should check the total water capacity of your pot before assuming that the pot will be measured in 6 oz cups.
If you have a pot that is overflowing the basket even after checking the cup size the chances are that you are either grinding too fine and clogging the filter or your coffee pot manufacturer has decided to make their filter basket a little smaller than normal. If the issue is a small basket your best bet it to figure out how much coffee the basket will hold and add water accordingly. For example, if your filter basket only holds 8 scoops (16 tbsp) without overflowing fall back to 48 oz (8 x 6 oz cups) of water.
Ultimately the amount of coffee to use is a personal taste but I highly recommend at least starting with the standard and adjusting from there and donâ€™t forget as you move toward more water and less grounds you will extract more off flavors. Most people that say they don't like strong coffee mean they donâ€™t like bitter coffee and weak coffee actually has more bitter compounds. You can always add hot water to weaken coffee. Weak coffee if just weak coffee and can not be fixed.
In response to a question in the comments below I grabbed a few antique coffee cans in my collection to see what the "historical" recommendation for coffee amount was and the recommendations are far from consistent.
Chase & Sanborn, Del Monte, Yuban, and Butter-Nut have no brewing directions of any kind.
Luzianne (Coffee and Chicory) suggest one heaping teaspoon per cup. The cup size is not defined. See my notes below.
Kaffee Hag Coffee (Decaf) recommends one "well rounded" tablespoon per measuring cup (8 oz) of water.
Maxwell House and Sanka (Decaf) both stipulate 2 level tablespoons per 6 oz of water.
One rounded and two level table spoons are not drastically different. I'd guess one "well rounded" tablespoons is maybe one and a half level tablespoons. The real outlier here is Luzianne at only one heaping tablespoon per cup. Chicory would account for some of that but not the complete difference. I cut maybe 25% when using chicory coffees but not the ~75% this would seems to recommend. My only guess would be that chicory is a historical coffee stretching agent so maybe there is also an element of people becoming accustomed to making weaker coffee to also extend the can of coffee but that is a pure guess on my part.