First AG batch, and first Starter question

Doing a 5 gallon Bells Oberon batch as my first AG, and decided to try to harvest their yeast from the bottle. I took the dregs from 3 bottles of 1 week old Oberon and made a starter out of 1/2 cup DME and 1 pint of water, boiled about 10 min, cooled and added both the dregs and wort to a 1L flask. Ended up with about 400MLs of fluid. Took a couple of days for krausen, then i cooled and decanted.

Then i stepped it up with 3/4 cup DME and 1 1/2 pints of water, then added to flask for a volume of about 650ML. Fermentation started within 5 mins.

Now my question is, should I step it again? Or should I have enough yeast slurry? Plan on brewing Wednesday. Also, should I have some back up yeast on hand incase it doesnt take off. Thanks

Bump

I'll be interested to hear an answer too. How do you know how many yeast cells you have to pitch? I guess if you decant And the. Just measure what's left in a measuring cup then is there some conversion from say a 1/2 cup of yeast slurry to cell count?

I ended up stepping it up one more notch, but didn't get much more trub out of it. Ended up pitching the whole starter (1L).with airlock activity within 12 hours.

Update...... This was my first AG, and messed up a couple of things, one being too rigorous a boil. I endend up with about 4.5 gallons of cooled wort. I just took a sample after 10 days of primary, and got 1.012 FG, which according to the calculater, is 76% attenuation using the above method. I plan on washing the yeast, and getting a few more batches out of those three bottles of Oberon.