Hi Joe! Congrats on making it through surgery.
The numb patch you mention is quite normal; a peripheral nerve gets cut during the surgery, and leaves you with a numb patch that may or may not eventually resolve itself. (I was told it would eventually shrink to a point where it wasn't noticeable, but mine is still there nearly 9 months after surgery.) You'll probably also find that you start to get some odd sensations in that area when the nerve starts to regenerate - tingling, prickling, hot and cold.
With regard to your questions about e-stim and working the knee out, you need to see a physiotherapist for a proper rehab program and advise on when to begin working the knee. Correct rehab is absolutely critical to the success of an ACL reconstruction, and it's very surprising that you weren't given instructions about this before leaving hospital. I can't stress the importance of this enough; in the early days you have to be very, very careful about what you do because the ACL graft is weak and you need to protect it. Additionally, you need to make sure you're not doing anything that could compromise the meniscus repair. Over time you can gradually introduce more exercises, but when and what depends on the kind of graft you have and the progress that you make. You can check out the Information Hub for some examples of ACL rehab programs to give you an idea what to expect.
Generally for an active job you could be looking at anywhere from 3-6 months before you can go back to work, depending on your progress. Again, it's really odd that your surgeon gave you no guidance on this. It seems like you're missing a lot of important information - I would strongly recommend calling your surgeon's office and asking for some clarification around rehab and return to work expectations. A successful ACL rehab has some very specific requirements, so you definitely don't want to be guessing at what you should and shouldn't be doing.
Best of luck! I hope your rehab continues to go well.