Is it difficult to repair a blown head gasket yourself?
If you're of average mechanical ability and the job doesn't have snags, no. If you're going to tackle it, do exactly what you're doing for starters: research. Get your specs that are needed as well as a r&r procedure, and you're off. Depending on where you live, or more precisly, where the car has lived, you may need Torches. The "manifold to head" bolts can be challenging, but shouldn't stop you from trying. The bigger question you face is "is it just a head gasket?" It is possible that the gasket may have been blown from warpage in the head, in which case the head should go to a machine shop for cleaning, pressure testing, maybe magna-fluxing for cracks, and machining if it is okay. You could put it together and still have a problem. So send it to a machine shop unless you are just going to get a reman head. I don't know what size engine you have, so I can't get too specific, I would guess a 2.2 or 2.5. Fair chance of a cracked head if so. Tightening specs and sequence are important for the head bolts. Plan on new ones, toss the old ones. Get a new thermostat while you're in it. Overheating can damage a thermostat. Getting back to the original question, yes, you can do this, be pateint. IF a bolt snaps a machine shop can help you. Continue to research this before you start. Good luck. It depends on the car. Years ago I did it every Friday night on a Corolla for a month - took about 4 hours. Then I finally realised the head was cracked. Overhead cams make it more tricky. For example, on some cars the cam chain has a tensioner located low down. The chain must be kept under tension the whole time, or the tensioner falls into the sump. Then it's off with the sump. A full maintenance manual giving the procedure and specs for clearances is essential. Of course, a tension wrench is a must. It's best to do this with someone experienced the first time. However, with the right tools, maintenance manual, and common sense, it's not too difficult. As with any car repair, have a few plastic containers for nuts and bolts, each labled. Otherwise expect to have a few left over at the end - not nice. Note that what seems like a blown gasket can also be a warped or cracked head. Get this checked out before re-assembly, particularly if the car has overheated.
A blown gasket can be repaired by replacing the gasket...if you are talking about the head gasket, then you have to remove the cylinder head from the engine block and replace the gasket that is inbetween them. Cracked heads generally have to be replaced because they are made of aluminum which cannot be repaired permanently once it is cracked.
A thermostat gasket is a gasket for a thermostat, a head gasket is a head gasket. The top part of the engine needs to be disassembled to repair the head gasket. You can find information on your specific car in your local library. You may even be able to access this online if the library has the databases available.