Look in your owner's manual to see which plug to use. Generally you should use a Bosch copper plug (not a platinum!).
I've never had to gap any Bosch plug recommended for my 300E, because they already had the correct gap. However, it wouldn't hurt to verify they were correctly gapped.
Your engine should take a tapered seal spark plug torqued to 10 to 20 NM.
Get yourself a can of HD silicon spray and spray the inside of the spark plug wire boot before putting the wire on the plug. It will make it easier to get the wire off next time w/o damage.