How do I keep track of receipts/expenses?

You should keep the receipts in relation to your business expenses for five years from when you lodge your tax return in case of an audit.

You may find the ATO myDeductions tool helpful for keeping all of your records in one place: https://www.ato.gov.au/General/Online-services/ATO-app/myDeductions/

You may also use Airtax Receipts to upload your expense receipts: https://help.airtax.com.au/hc/en-us/articles/360000117415-Airtax-Receipts