I have never made any kind of count to cut the sprue. Another learning curve, watch the sprue puddle and when you see a flash over the sprue is freezing. The sprue can be opened with a gloved thumb, if you need to whack it to open you waited too long. If you smear lead you were too quick.
Good advise. But, if you have 4 or 5 cavity molds, chances are the first couple of sprues are rock hard by the time the last sprue frosts over. A mallet or similar will be required unless you have ape hands.
I suspect you will soon grow weary of standing over a hot propane stove and will upgrade to an electric furnace. If you think casting is something you will continue to do, go buy yourself a hotplate. You set it for a medium heat and put your mold on it while you are waiting for the lead to come up to temp. First bullet out of the mold will be perfect. I also set the mold on the hotplate when I replenish the pot and wait for it to come back up to temp. Mold will be ready when the pot is.
I think I missed your initial post. If this has already been mentioned, please excuse. Cast iron ladles and anything with a flux deposit left over from the last casting session will probably have absorbed moisture from the air. DON'T DUNK EITHER INTO THE MOLTEN LEAD! If there is moisture present, it will flash to steam under the surface of the lead and create a small explosion that can spew molten lead everywhere. When you start a session, dip things in slowly. Any moisture will make itself known with a popping sound. GO SLOW until you can submerge the entire item. Now you are safe.
Get a good pair of full coverage safety glasses. I like the kind you see in factories for visitors that fit over regular glasses. They have side shield for added protection. I suggest leather gloves as well. You don't need welder's gloves. Just something to protect your hands. Everything will be HOT!
Happy Casting