How to track inventory for a tire shop

Hi my name is Kevin and i am new to this forum. I have a question about tracking inventory and cash flow for a tire shop. To sum things up me and my wife had this and another business passed down to us. This business brings in alot of cash flow. Right now i would have my employees do the service, but i would take the money from the customers. I am planning on expanding and doing so i won't be around to get the money from the customers. I would like to figure out a way where i can keep track of our inventory and cash flow when i am out doing business. I currently do not have a POS system. So to sum it up my questions are

1) how to keep track of inventory.

2) how to keep track of cash flow when i'm not around to see if money is missing.