If the ebay NOS machine that you posted earlier is to be believed, they came with two stones--can't say for sure. You can search for "Ring Test" on google to see how to check whether your stone is compromised, but no one will fault you for changing it to be on the safe side.
Both stones and wire wheels will last in accordance with how and how often they are used. If you are grinding the **** out of hardened steel on a daily basis, things are not going to last as long as if you just sharpen a chisel or two when they get dull. It's hard to really wear out a wire wheel unless you abuse it.
Like stones, wire wheels come in graduated coarseness to effectively deal with different applications. Your 36 grit stone is coarse and is designed for removing material quickly. Like sandpaper, the higher the number the finer the grit and the smoother the grind.
Without knowing what you intend to use your grinder for, no one can say with certainty what the best wheels would be. For occasional garage grinding chores, a medium 80 grit will usually work well combined with either a more coarse or less coarse second wheel, depending on what you need.
To cover all the bases, you may need more than one grinder!
And don't forget--you need to balance your wheels just like a car. Otherwise excessive vibration causes excess wear, noise and makes smooth grinding more problematic. You can google how to do this, too.
Good luck and happy grinding!
