Some noob stirplate and starter questions

After viewing many threads I built a computer fan based stir plate.

On my last visit to the LHBS I bought a stir bar and a 1 litre flask. (They have 2 litre flasks on back order)

I harvested about 2 teaspoons of yeast slurry from a local micro brewed hefe. Pitched it into 500ml 1040 wort and ran it for 24 hours.
I cold crashed it and repitched the now 2 tablespoons of yeast into a fresh 500ml starter. (Only 500ml because i'd hate to have an overflow)
Cold crashed and repitched again.

I then pitched half of the cold crashed yeast into a 1 gallon trial hefe.

I think I fermented that too cold (55 to 60 F) The end result wasn't bad beer, but it wasn't quite what I was aiming for.

Time to do it again, but I have some questions about the stirplate and starter process. I pitched the refridgerated yeast into a fresh starter solution yesterday and it hit high krausen within 2 hours. I let it run for another 10 hours before i cold crashed and cleaned the equipment for todays second step. Again it took only about 2 hours to reach an amazingly high high krausen.

Now for the questions. Is it nessasary to let it run for another 10 or more hours?
Because my flask is so small, does it make sense to split the yeast at some point and make two 500ml starters? (5 gallon batch at 1045-1050 predicted OG) I do plan to hold back a tablespoon or so of slurry again.
Would it be a good idea to ferment the next beer a bit warmer, say arounf 65-70f?

From this thread https://www.homebrewtalk.com/f163/commercial-beer-yeast-harvest-list-262713/

I got the following.

LVBen said:

barhoc11 said:

I guess my question is, how do you know when you have enough yeast?

Click to expand...

The best you can do is estimate. The yeast doubling time (under optimum condition) is 1.5 to 2 hours.

If you have a very large quantity of yeast cells, then you won't get that kind of speed. It might take a whole 24 hours to double.

If you have a small amount of yeast (like the small amount from a few bottles of beer), then you'll get closer to the 1.5 to 2 hours of doubling time.

Under perfect conditions, you could theoretically go from 1 yeast cell to 100 billion yeast cells in just 3 days.

There is usually way more than 1 yeast cell in the bottom of a bottle-conditioned beer, but on the other hand, our yeast is not in perfect conditions.

So, what I do is check to see how long it takes for the starter to drop from the OG to the FG. If it takes longer than a day, I decant the liquid off the top and add fresh wort. I'll do this until I can get the starter wort to drop from OG to FG in just 24 hours.

With the Chimay White bottle, it took me about 1 week, and I replaced the wort 3 times.

Mathematically, using 6 bottles instead of 1 will only save you about 4 hours.

Click to expand...