don't know...

"so much" is informal and shouldn't be used when writing. "Really" and "very" can be used in the same way as adjectives, however you can just use 'very'. Really? Can be a question, asking if something is true: Really?

Here's an example of a subtle difference between "Really" and "Very"

"I am really angry." (My anger is serious and shouldn't be taken lightly.

"I am very angry." (My anger is intense.)

They can be used interchangeably in this way, and both can answer teh question "How angry are you?"

On the other hand:

"I would really like to go to the park." - This expresses the strength of the desire, i.e. how much you you would like to go.

"I would very much like to go to the park." - This sounds awkward and old fashioned. You might find sentences like that in older English books like "Alice in Wonderland".
It sounds more natural to say "I would like to go to the park very much."
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There's really no difference. You wouldn't sound weird or awkward if you think they're all the same. You should feel relaxed, they're all used very often and naturally. "I love you very much"=I really love you= I love you so much= I love you a lot. 大好き、好きよ、好きだ、愛してる、あなたが大好き、あなたのこと大好き。 It's all the same, nothing to stress over.