You can certainly make your own starter wort. A couple of things to remember- coming out of the MLT, it is still likely contaminated with lactic acid bacteria, among others. So, you definitely have to boil it before saving it. Now, if you pressure can your wort, you can skip the boiling at this stage and just can it as long as you do it right away. If you wait, you'll end up with a lacto infection and some sour starter wort. Even though boiling will kill the active bacteria, the sourness will remain.
What I would do is to just make a 5.5 gallon batch of beer, and save some of the finished wort for starters and stick that in the fridge or freezer. I find it's just easier to buy DME and make starters with that.
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