I systemize and automate businesses end-to-end for a living.
Don't despair, this is a bit of an art and it's slowly becoming a science.
I have largely virtualized my consulting practice that I have run for 10+ years using remote developers both locally and out of town.
This is a problem I have obsessed over solving the past 12 years. It was hard enough to get it working in-house with employees, to learn the key qualities needed to make it work from anywhere.
There are a few key things you must solve:
0) KNOW YOUR PROCESS.
Are you able to take all the steps of your process and lay it out on a flowchart, no matter how complex?
Can you take any request currently in your business and place it on this flow chart?
Once you can do this, you are ready to systemize. Until then, this is where you are needing to clarify and build out things.
1) A CENTRAL SYSTEM THAT HANDLES YOUR WORKFLOW.
There is no magic ONE tool that will solve anything. Most suggestions will be helpful with one or a few parts of the process. Instead you will need to connect multiple tools to get what you need.
The key is having a central communication system.
It doesn't sound like you have this yet. This is a non-neogotiable.
The communication system must be based around requests/cases. All communication, regarding work people need to do, needs to be in this system. The cases need to be run through a fulfillment process that captures and reflects your competitive advantage.
2) DOCUMENTATION IS YOUR FRIEND.
Documentation can suck, royally. Meaningful documentation is even harder. But it's the only thing that allows people to answer their own questions. Being able to capture your intellectual capital and spread it is critical to having your business grow.
If you're having trouble teaching, remote workers are having a hard time remembering. The key is to create a culture of self-serve updating documents. A wiki is often critical for this, however I am also a _big_ fan of videos integrated.
3) BUILD YOUR TIME / BILLING TRACKING INTO THE BREAD.
Billing, and time tracking, also sucks. Whatever unpleasantness we don't want to deal with now has to be dealt with doubly later.
It's best to bake time tracking/billing into the bread and your process. With the right configuration based around your process this is pretty possible.
If you have to track billing/time for this, it must be a simple, usable, system that is hopefully integrated right into your system. I am a quickbooks guy for most of my stuff, however I've started using Freshbooks for the Accounts Receivable / time collection side of my business and it's working a lot better.
If you have a process but works and just lacks in being clearly explained / taught, I can help you with that. Reach me by email or ask any questions here. I guarantee results if you're willing to do what's needed.