Is “so” different from “this” in these sentences?

Question

Here are the sentences:

It was only so long. It was only this long.

Is your dream only so big? Is your dream only this big?

I think they’re the same, but with different feelings that I couldn’t describe.

Answer 1

Your examples of

so
this

has a difference in nuance. Both mean that something is limited.
By using "so" it is indeterminable in where the limit is: maybe a foot, maybe two feet. Using "this" has a specific limit. However with additional context, both "so" and "this" may have exactly the same meaning.