Where does majority of the energy for the magical effect of a potion
Does it all comes from the brewer? Or does most of it comes from the ingredients?
I don't know where does the majority of the effect come from, but at least we do know that spells are usually required. I suppose that it really depends on the potion you're working on - I don't think a spell is required for all potions.
I know JKR said that you have to use magic at some part of the process of brewing (hence no muggle potion brewers) [what about a
I think it is clear, then, that it simply sucks for squibs. Which makes sense. This may contribute to explain why is Filch so inefficient identifying potions.
If brewer provides all of the energy then why aren't NEWT students magically exhausted after every potion class?
I don't think they explicitly mention whether students were tired or not after their potion classes. They probably were, but that would most likely be because of, uh, studying hard? XD
Hermione successfully brewed batch of Polyjuice Potion (a very potent NEWT level potion) in first semester of her second year, and
while brewing it was very time-consuming and required a lot of
concentration she never showed any signs of exhaustion as far as I
Brewing that potion takes several weeks/months/whatever. She had plenty of time to rest. I think that this proves that the longer a potion takes to be made, the least exhausting it is, because most of the time it consumes is, well, waiting rather than casting spells on it too frequently. For this kind of potions, the highest requirement would probably be patience and intelligence - Hermione should do fine.