Hello Raymond,
I also prefere removing the engine and transmission together. However it can be done both ways.
One important thing to remember is to disconnect the torque converter from the flywheel before attempting to separate the engine from the transmission.
Now for the top bolts; your mechanic is mostly correct. I like to use 1/2" swivel end extensions actually about three to four feet of them linked together. The bolts themselves are not 15mm but 17mm. You will not need a flex socket with swivel extensions. Also remove the transmission tunnel cover plate (passenger side) to give good access to the starter bolts (10mm allen) from inside the car!
Joe Alexander
Blacklick, Ohio