wait......this is a new purchase bike, after 2 years (unknown mileage) you want to
change BOTH chain and cassette?

have you measured the chain "stretch"?
what is the condition of the cassette cogs?
maybe just need a new chain.


don't worry toooo much about getting the most mileage out of them.
they're consumable expendable bits.
keep 'em reasonably clean, replace as needed.

you "should" get 2000-4000 km from a chain, depending on conditions of use.
then change the cassette every 3 or 4 chains.
not really worth obsessing over.