Honestly - - custom software is a terrible idea for a business that's doing less than £10 million ever year,... custom software is either VERY expensive, or plain rubbish.
Many people don't realise that as well as the huge development cost, there is a huge ongoing cost to keep it up to date with current standards, device compatibility, security protocols etc etc - as well as adding new features that a growing company will need.
My advice would be to find an off the shelf solution that is as close as possible to what you need & approach the developers asking if they'd custom code your additions - - it'll cost less, be more stable - and if you allow the developer to share these additional features that you paid to develop with his other clients, you'll probably see your new module receiving regular updates and feature additions without any ongoing cost to you....
I'd ask Rob at Cleaner Planner for his advice - maybe talk to the guys at Aworker too if thats the system you already use,...