Install a timesert. Its a bit better than a helicoil. I just went through this on my kx. Previous owner installed a helicoil and it doesnt hold the oil at operating temp. Had to use that white plumbers tape to fix it. A timesert looks more permanent and doesnt have a bunch of little slits oil can pass through. That being said tons of people still have good luck with helicoils.
As far as tapping, youll want to use the correct tap drill. Get some tap lube or wd40 and turn the tal in as straight as possible. Go 2-3 turns and then back put, go 2-3 turns again, back out, until youre at the depth of threads you need. If it starts binding just back the tap out, clean it up and put more lube on. Pretty simple.
2009 Kawasaki KX450F
2009 Kawasaki KX250F
2002 Suzuki GSXR 600