First implement the graph.rs file, make sure you pass all the tests. Write your own tests for complicated cases. Try to finish this by next Monday without fail.
Download the blocks from [start_height, end_height] inclusive. Build the graph
as explained in the build_transaction_graph function of profile_transactions.rs file.
Write some tests using Regtest node to verify your implementation works correctly.
Use bitcoind crate to start the bitcoin crate programmatically
in regtest mode.
This test might be involved and will require patience and lots of thoughts from your end.
You can take your time for this.
Also learning to test like this is a valuable skill that you will require to build production ready bitcoin applications in Rust.