Is there an app or anything that would allow me to save the receipts for the projects I do? how do you save your receipts? Or does everyone just use a big folder?

I have a Network Attached Server (RAID enabled with 5 hard drives) with 10GB of space.  I have other business ventures that take up a lot of that space.  It's backed up to Google Drive.  That's how I store my stuff.

With relation to how to store receipts, I scan them in as a PDF file and then name the file by date and vendor.  As an example, if I had to pay a plumber on March 18, 2018, the file name would be '20180318 XYZ Plumbing.pdf'

I also use Xero as accounting software....I upload a copy of the pdf and attach it to the transaction in Xero.

...this leaves me with three copies of the receipt, a way to retrieve the receipt by data and by vendor, and a system that works for me.

Use Microsoft Onenote, you can create notebooks 9 maybe name it " Properties", in the notebook create a tab for each property, then you can have different pages for each tab, you can make one page " Receipts" for that property. you take a picture, save it to the page for whatever property in one note, with the APP on your phone. you can save them directly to that page, create Receipts pages for each property. and you can retrieve that information on any device that has Onenote. you can even name each page by the year if you want " receipts 2018" and you will always have your records anywhere you go.