I have used two different methods for cutting the top off a Sanke. On my first one, I used a dremel to quickly draw my cut line and then used a full sized angle grinder to cut through the top. If aesthetics are a non-issue, this is a VERY fast way to accomplish the mission. I did however have to shave my face 2-3 times to get all of the steel filings embedded in my face out ( I was wearing goggles of course). It also leaves soe rough edges and gouges due to the fact you are cutting with a wheel that has and inch or two of a straight line in contact with the cutting surface instead of a single point like with a plasma torch. It functionally did the job and doesn't look too bad either.
I just cut a keg out for a friend this past weekend with the Dremel. Dremel makes a cutting wheel kit that comes with the fiberglass wheels, some wide discs, the small extra-hard cutting wheels and this afro buffer pad. I used a combination of the wide cutting discs, the small discs (which cut through about 5 degrees of the total 360 degrees at a time) and the fiberglass reinforced discs. The method I found to be most efficient is to use the wide discs first and not cut all the way through but make a thick cut line around the top. Then come back with the thinner fiberglass wheels to finish off the job. It was just takng too damn long with the little wheels!!!!! I then run a sandpaper cylinder attachment around to get off the big burrs and finally used up the entire afro buffer wheel smoothing the edges. I was VERY happy with the results from this method and did the whole thing in half an hour. Always make sure you fully depressurize the keg. It was sad dumping 4 gallons of leftover Yuengling (that actually looked to be fairly fresh) down the drain.
For my side holes, I use a hole saw, drilling an initial pilot hole with a regular drill bit and inserting the bit of the hole saw into this pilot hole. It cut through the side very quickly and left a nice edge. No leaks on weldless fittings.