Conclusion: no comma usage is absolutely required with “therefore.” Use a comma only if you want to slow the rhythm of the sentence and/or emphasize “therefore.”

Is therefore redundant?

Senior Member. "So therefore" is not idiomatic and would definitely be redundant in the examples you presented.

What is the meaning of I therefore conclude?

(used to introduce a logical conclusion) from that fact or reason or as a result. “therefore X must be true” synonyms: hence, so, thence, thus.