The main definitions of goodly are (1) quite large or considerable, and (2) of pleasing appearance. The second sense is rarely used today. Despite the -ly suffix, goodly is not an adverb. Good’s corresponding adverb is well.
Goodly does not traditionally mean helpful or benevolent. For these senses, consider kindly, another rare -ly word that functions as an adjective (though kindly does also work as an adverb).
Examples
Back in biblical days, the holiday’s menu no doubt included a goodly number of grain-based dishes. [Los Angeles Times]
Yet a goodly number of readers—and several opera afficionado friends—were underwhelmed. [Vancouver Sun]
I know I’ll now be forced to spend a goodly part of my life asking people if they’d like to see my wenis. [Southland Times]
John died of lung cancer in 2003 and left a goodly chunk of the Bacon estate to David Edwards, his beloved older brother. [Daily Mail]