The phrase "a plethora of challenges" is correct and usable in written English. You can use it whenever you want to express that something has a large and diverse selection of challenges, difficulties, or obstacles. For example, "The new software project faced a plethora of challenges, from technical issues to budget constraints.".
Two politically divergent experts concur in recent books that the United States will remain the globe's top dog despite a plethora of challenges and a governing class not fully up to them, and despite the spectacular rise of other large countries.
For anyone tempted to take ownership of an empty estate, a plethora of challenges await.
With the expected arrival of a baby, all working mothers face a plethora of challenges.
Unfortunately, a plethora of challenges plague the agriculture value chain ranging from cultivation to retail.
Through each passing day, my blackness undergoes any plethora of challenges.
These often competing drivers create a plethora of governance challenges.
While life on land presents a plethora of other challenges, the last we will look at here stem from the physical differences between water and air.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union