A comma is placed after adverbs that are also conjunctions. Thus, therefore, consequently and many others =LIST HERE= are conjunctive adverbs. e.g. I had spent all my money, consequently, I could not go out to eat with friends. I ate a big lunch. Thus, I was not hungry later that after
Such things are often to some extent matters of custom.
Howver, remember that a comma simply represents a pause in speech.
When I consider how I would say sentences using rhese words, I find that I would commonly pause after the other words you mention, but not after 'perhaps'. Perhaps the word 'perhaps' is more closely associated in meaning with