A lot of the circular saw blades are alloy steel that is chosen to minimize warping when they heat up, or to provide a good bond for carbide teeth. Most of them are good steel for knives but since the composition is often unknown, you could spend some time experimenting to find the proper heat treating method. Alloy steel can be tough to grind as well.

The hand saw, if it is more than 20 years old, is most likely good carbon steel, probably around 1% carbon. I have never, yet, had a problem making a knife of handsaw blades. The blade will be a bit thinner than that of many knives but often the thinner blade will be easier to grind and keep sharp.

It is extremely important to keep the blade cool when you are grinding. A grinder with a water spray is not essential but it will speed up the grinding process by a factor of ten.

Also, if you have a steel supplier nearby, you can order 1095 steel in a variety of strips, sheets and bars. That way, you can have a blade as thick as you want. Costs though.

You might want to look up some information on heat-treating carbon steel. If you heat-treat properly, you will have a tough blade but one that will fiercely hold an edge. You will want one that covers annealing and hardening. I have some references on the subject but they are down in my shop building. If you would like, I'll send you the author and title once I get down there. Just let me know.

Have fun, it is really satisfying to use a knife you made yourself.