Breakdown of Poza tym mam dużo pracy.
mieć
to have
praca
work
dużo
a lot / much
poza tym
besides, apart from that
Questions & Answers about Poza tym mam dużo pracy.
Why does this sentence use tym after poza?
The phrase poza tym is a set expression meaning "besides" or "moreover" (literally: "beyond that"). The word tym is the instrumental case of to (this/that). The preposition poza requires the instrumental case when describing something being "outside of" or "beyond" something else.
The verb mam usually takes the accusative case. Why is pracy in the genitive case?
You are right that mieć (to have) normally takes the accusative case. However, the word dużo (a lot) is a quantifier, and in Polish, quantifiers force the noun that follows them into the genitive case. The rule for dużo overrides the rule for the verb, so the base word praca changes to its genitive form, pracy.
Could I use wiele instead of dużo in this sentence?
You can, but dużo pracy sounds much more natural for everyday conversation. Dużo is generally preferred with uncountable nouns (like praca or czas), while wiele is usually reserved for countable plural nouns (like wiele pytań - many questions).
Could I use oprócz tego instead of poza tym here?