#1 Here is a good link for calculating starter wort.
The bottom line is not to exceed 1.040 as it will stress the yeast and will not create optimal conditions for growth, so anywhere in between 1.020-1.040 is recommended.
Also some would say go ahead and make a 3-10q/l starter but the majority will agree that for optimal growth you should step up towards big cell counts. IE: If it were me, I would make a 1-1.5L starter and add a second or third feeding if necessary 24-48 hours after each step if making a simple starter.(See below-now referred to as shaken starter in this conversation.)
In this case their are two things you will learn. #1 is to select shaken starter in the radio bar within Mr malty. You will select this in the program and practice it in making starters. #2 What this means is after the wort is boiled/ cooled you shake it vigorously to infuse the wort with O2 because it has none after boiling. Then you shake/swirl the starter a few times a day to expunge bound CO2 and introduce O2. By doing this you are emulating what a stir plate does constantly. So you will now notice the Q/L requirement drops in the calculator.
So in this beer you need 1.86L with one pack to hit the 246b/cells you are seeking. Which is still fine to make in one step if your vessels accommodates. IE: 1L flask = .75L starter / 2L flask = 1.75L As you want to make room for foaming during boiling and the krausen during growth.
In this case I would simply make a one step 1.75L as it will grow approximately 239b/cells which is close enough. If you only have a 1L make .75L to grow to approximately 130b/ cells and then pitch a second wort of .75L which will hit the amount needed as you actually create more cells with the 1.5L split up in two steps than you would making 1.5-1.75 in a first step but this all depends on your exact situation and patience. But lets say you wanted to make a lager at 1.050 that calls for 368b/ cells then if using a 2L flask you would make the first step 1.75L = 239b/ cells then you would need a second infusion of wort of 1L to finish at 368b/ cells otherwise it calls for almost a 5L starter which is too big for one step as a rule and secondly it is a waste of DME when you could have cut it down just by doing it in steps which is not all that difficult.