I'm no finance expert, but I was always led to believe that overpaying is largely a waste of time depending on the interest rates, and you'd be better off investing the overpayment amount? that said I'm no expert! (I'm not suggesting you're wrong! It's more of an open question - please don't take it as a dissection of your post ),.
Regardless, that's a fantastic target and fingers crossed you're able to achieve it! Good luck
No, not on repayment mortgages right now.
You generally won't get the return on the investments Vs what you will save overpaying.