That's a mouthfull.
Question 1 - Depends how much botanicals you want to use. Are you
packing the column with the botanicals or boiling them in the water? If
boiling them the column length is more than adequate. If packing it the
longer it is the more you can fit in it.
Question 2 - Plenty of people use plastic boilers so long as the plastic
is thick enough to hold up when it reaches boiling point as it can get
floppy. The liquid absorbs the heat from the element during normal
operation but I wouldn't recommend boiling it dry as the temperature of
the element may quickly exceed the melting point of the fermenter.
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