The reason I haven't replied is because it is really quite tough to know exactly what to do in your situation without seeing it. These old plaster issues are usually a judgement call and different people weigh different factors differently. I am of the school that it is usually quicker, easier and better results by ripping out the old plaster, right to the studs and doing new drywall, etc. Say you have one wall. You lay down heavy cardboard or 1/4" ply to protect the floor, cover that with heavy cloth dropcloths, put a fan in the window blowing out, put on your gloves goggles and dustmask and go at it with a large prybar and hammers. You can have it down to the studs in less than an hour. You gather the big chunks and laff, pull up the corners of the cloth and slap the drywall up and you are good to go. Otherwise, you need to decide which area to keep the old and which to replace and patch in - use plaster washers to secure loose areas, shim or plaster to achieve a consistent level or plane of the wall , etc. etc. etc. and you still end up with a wall that can crack and not a flat surface. By the time you patch and fuss you could have just ripped it out and ended up with a nice new wall. The prybar and sledge are your friends!!!!! Don't forsake them. If at first you don't succeed, get a bigger hammer!
If you do patch you need plaster washers to secure loose areas. If you have big cracks to fill with mud make sure to use very good mesh or paper tape to prevent future cracks. I use quick setting durabond plaster mix or plain old plaster of paris for really deep dingers. It sets up in a couple minutes and lets you start on finish coats. Otherwise you will be waiting for weeks for the regular mud to dry. Be advised that quick setting stuff should be kept below the finish surface as it is next to impossible to sand away high spots - you don't want to go there.