When you start from underneath, just leave a long piece of thread. When you get back to that piece of thread , tie a square knot with the two ends you will have. Sorry anbout that, I thought I posted the picture of the square knot, but I didn't.
Yes, use one continuous piece of thread to make each repair.
You'll need a 4" 17 gauge curved needle from an upholstery supply place. CLICK HERE