Yes, they are standard threads. They are fine threads. Many mechanic's (and by extension I'm quite sure some of the ones in the military as well) are pretty convinced that half of a bottle of locktite is the solution for bolts that are prone to backing off, and torque wrenches are an old wives tale. Many are also convinced that "inadequate recommended torque" is the reason for the semi-common cracking condition that occurs in a lot of GM drive plates (regardless of the lack of evidence of movement under the bolts), and the other half of the bottle of locktite will fix that issue too. The real answer is "NO" in both cases, but don't be surprised if they may take more than a reasonable effort to remove.
Holding the flywheel can be done with a flywheel holder tool, available from your local tool trucks for a boatload of money (well, they're not that bad, but for one time use...?) They're probably available at larger parts stores or Sears. Or, you can "tack"the starter back in place with the two big bolts if it's removed (wires and braces are not necessary at this time, but need not be removed either) and wedge a prybar between the starter driven teeth and the nose cone of the starter. (Even the professional tools only hold it still by a starter tooth, so it's only half as butch as it sounds). Just hold the prybar straight so that you don't get a bending motion going on. They're resiliant, so if you see it start to flex, stop pushing and adjust your angle of course, but they are a "flex plate", and don't loose their shape "too" easily.
