The yeast will do fine, I'm guessing you have 1 gallon of juice- 1 pack of bread yeast, even poorly rehydrated will be fine. The yeast will rehydrate if you put it in any liquid, some methods (temp, liquid type, etc) are better than other, but really you should be fine with this.
A hydrometer is very useful, these can be mail orderd if you don't have a local home brew store(lhbs) near you. The 2 main uses of a hydrometer or other measuring device (like a refractometer) are to determine if the fermentation is done, and get an accurate measure of the acohol content - often called abv.
You can get an idea about finishing by taste and by other signs - like bubbling, but they are no where near as effective as a hydrometer. For your first ferment it is fine to not bother. But if you get hooked into doing this, it is very useful. I did many a beer kit without one, just letting time take care of things.