SME/Freelancer web app for tracking projects, timesheets and invoices

I've been working on a rough idea for a few weeks now planning functionality but before I take the plunge I was hoping I could get some feedback.

I want to create a web application that allows small business owners or individuals to track all the core things they need to run their business successfully (I first had the idea when I was working freelance and keeping track of the companies Id reached out to, or tracking time/billing on projects was a pain). There'd be 3 major areas to the site:

Projects:
Users can create projects which have milestones and task lists, along with integration with trello, there'd be a timer built into the project page that they can start/end to track the time worked, or log times manually. They can also specify and hourly rate which would auto calculate a total based on hours worked, or input a lump sum payment and have it work out from how many hours worked what the hourly rate for that project has ended up being (I had one lump sum project that after completion I worked out had effectively made me £11 an hour which was very disheartening)

Invoices:
Automatic creation and tracking of invoices based on hours worked/expenses accrued with notifications if an invoice is reaching its due date.

Company address book:
List of all companies you're currently in contact in with markers for if theres a project in process for them, initial contact made, follow up in x months etc, and the ability to add employees + their contact details for that company (I had a few where I was in contact with 4-5 people within one company which wouldve been made far easier if I just had one location I could go to get all the info I had for them).

Any feedback would be appreciated, I know there's a few big players in the market like Zoho Projects but I found it really clunky and confusing to use as an individual.