can you add to an existing outlet? i have one plug in my garage shop and added one additional plug already. They wont always have things plugged into them, i just need more options. there doesnt seem to be more than one or two plugs on the circuit at the most.

What amp breaker is tied to it? What size wire is run to it? It is not the amount of options it is the capacity that is being used on the line.

good question, i think its just standard romex type 3 wire run from the house breaker

Rule of thumb 12 Ga wire is good to 20 amps. 10 Ga is good to 30 amps.

Usually you only want 8-10 individual lights and recpts on a circuit. (I think code is 12) With that said count everything on the circuit if less than 10 you should be able to add another recpt, don't count switches just the lighting and recpts. If your running large appliances, pumps or motors you should go ahead and add another circuit.

To answer your question as you asked it, put what you need. IF YOU ARE NOT GOING TO USE THEM ALL AT THE SAME TIME! In my workshop, I have six plug strips, one on each wall. I can plug in all my shop tools, but run no more than two at a time, and if I'm using the table saw it is the only machine on that circuit. You will learn what you can use, the breakers don't lie.

As stated above. You can add as many as you want. It's the amount of draw at any particular time that you must pay attention to.

the exception to this is if anything happens that requires an insurance claim it will be denied if not to code.

Good point if you are hard wiring outlets, but there's no code for plugging in power strips.