and so vs then

and so is not a noun while then is a noun.

Word	Noun	Adjective	Verb	Adverb
and so	No	No	No	Yes
then	Yes	Yes	No	Yes

As adverbs, and so and then are synonyms defined as:

and so and then: subsequently or soon afterward (often used as sentence connectors)

Other synonyms of and so include so.

and so (noun)	then (noun)
	that time; that moment

and so (adjective)	then (adjective)
	at a specific prior time

and so (adverb)	then (adverb)
subsequently or soon afterward (often used as sentence connectors)	subsequently or soon afterward (often used as sentence connectors)
	at that time
	in that case or as a consequence