IMO there is no need for a 10L starter unless you are brewing barley wine on a barrel system. You can make due with 1 smack pack if you have a stir plate. With the stir plate you are able to maximize yeast production and therefore will not need the 2nd package of yeast. You should be able to get one doubling or so out of your yeast in a 2L starter. That means if you start with a 100 Billion cell smack pack and make a 2L starter, you will have 200+ Billion yeast cells.
Here is how I make my starters:
1. Make a 2L starter with 1.040 OG (2 cups DME, 2L water, boil 20 minutes with yeast nutrient)
2. Pitch yeast into starter at 70°F and place on stir plate for 2 days
3. Cold Crash for 12-24 hours
4. Decant off liquid (I use my ranking cane and leave about a 1/2 inch of liquid above the yeast cake)
5. Swirl yeast into slurry and repitch into either:
a) another starter or
b) your wort
It is common for people to make their yeast starter 5 days before brew day. The yeast in the starter will consume the sugars within 24-48 hours. Your yeast undergo added stress if left in the starter after the sugars have been consumed. Also, be carefully not to pitch your magnetic stir bar into your wort either!