You should use a yeast starter for all brews that has an original gravity of 1.060 and above.
1. I use a similar DME as what is being used in that batch. Mixing ½ quart of boiled (cooled) water and ½ cup DME. This should give you a gravity of around 1.040, perfect for the starter.
2. Using the actual malt will give you a much higher gravity then you desire. Remember, you are making a yeast starter because your wort has such a high gravity. Think of it as preparing the yeast for bigger things.
3. I recommend a yeast start for any wort that is 1.070 and above, even with the smack packs. It is easy to do and really does contribute to the flavor of the higher gravity beers. Below is so pointer on when and how much to use.
This Pitching Rate Calculater is very handy.
Mr Malty Pitching Rate Calculator
If you're curious, here is the simple math to calculate the number of cells needed. For an ale, you want to pitch around 0.75 million cells of viable yeast (0.75 million for an ale, 1.5 million for a lager), for every milliliter of wort, for every degree plato.
(0.75 million) X (milliliters of wort) X (degrees Plato of the wort)
• There is about 3785 milliliters in a gallon. There are about 20,000 milliliters in 5.25 gallons.
• A degree Plato is about 1.004 of original gravity. Just divide the OG by 4 to get Plato (e.g., 1.048 is 12 degrees Plato).
So, for a 1.048 wort pitching into 5.25 gallons you need about 180 billion cells.
(750,000) X (20,000) X (12) = 180,000,000,000
As an easy to remember rough estimate, you need about 15 billion cells for each degree Plato or about 4 billion cells for each point of OG when pitching into a little over 5 gallons of wort. If you want a quick way of doing a back of the envelope estimate, that is really close to 0.75 billion cells for each point of gravity per gallon of wort. Double that to 1.5 billion for a lager.