He has overcome numerous hardships.
He overcame numerous difficulties and succeeded.
Many ancient documents are preserved at this temple.
沢山 is the common, casual word for 'a lot/many', whereas 数多 sounds old-fashioned and is mainly seen in literary or formal writing.
多数 is a neutral, still-current noun for 'a large number', while 数多 carries an archaic literary flavor for the same idea.
僅か means 'a few/a slight amount', the direct opposite of 数多's meaning of 'many/numerous'.
few-body system
Compound of 数 (suu, 'number') and 多 (ta, 'many'). The reading すうた is a Sino-Japanese on'yomi combination.