First, you can mark an app as Personal Use, deploy it and you should be allowed to use the app normally, including all features under the Core plan - I believe including notifications to customers. You can read more about that in this post.
About the app…
I understand that this is a small app (in usage terms) used only by you for which you record a few of your customers. But what if this small business venture expands? You want to be ready for that in some way and with just a little extra effort now you can be set for that future growth. I assume you would like to see this business grow, so…I recommend thinking of building this app as if it is for an already well established business model.
Where to start in app re-design?
Understand what real-world “objects” or “entities” your app interacts with and determine what details you want to collect under each. Each of these collections translates into your “core” data tables. For example from reading your post, I see you have these potential tables:
Cars - assume you will eventually have more than one car. For these cars you’ll likely want track the Make, Model, Color, License plate, Active, etc.
Drivers - obvious - Name, Location (driver address), Driver License #, Reimbursement Balance (amount to be paid to driver)
Customers - the individuals paying for services. Name, Location (customer address), Payment Method, Balance, etc
Locations - use this table for ALL addresses. It will ensure the address is entered only ONCE and is represented exactly the same each time used. You can then easily track the most frequented Locations - Location Name, Address
Trips - details about each paid trip taken - Customer, Car, Start Location, End Location, Distance, Number of Passengers, etc.
Trip Payments - a transaction for each paid trip - Customer, Trip Cost, Customer Starting Balance, Driver Payment, etc
Driver Payments - a record of the transaction to Reimbursement Balance
Replenishment - transactions that add to Customer balance - Customer, Replenishment amount, Payment Method Used, etc
There will be other columns of data you wish to track. There may be other tables you need as your core data. There definitely will need to be additional tables used as utility or supporting tables. Don’t hesitate adding more tables if they help facilitate an easy to use AND easy to implement app.