I understand your point, but that's not how things work.
If you source the right ERP you will be presented with procedures and processes that have been streamlined and optimized leveraging previous experiences of literally hundreds of businesses. Smaller and larger than yours. It's an error to dismiss the standard solution without deep consideration.
Any process into a good ERP (e.g. managing a deposit payment, managing stock, documents transformation, uniqueness of product codes, and so on) is battle tested and may be ready to solve issues that at the moment your company in not seeing, but perhaps will have to face with the growth of the next five years and in five years perhaps you'll see the reasons why things were setup that way into the ERP.
I have been happily humbled more than once by that.
Check how things are supposed to work into your ERP, understand them and comply. That's how to have a functioning ERP in your company. Or just don't buy it and go for excel, it's cheaper (but just at the beginning, be warned).
Just to add... a lot of processes are very defined. I know HN loves to startups that reinvent the wheel but things like GAAP are pretty much the same workflows in any biz. AP, AR, SO, POs, etc.
