Re: the fuse, hopefully I haven't recommended something for which I can't give you the right answer! Here's what I know: Normally, fuses are used to protect the house wiring (i.e., prevent burning down the house
); however in this case, we also want to protect the battery or PS from an accidental short circuit on the breadboard. Several things to consider are wire size, maximum load, and the output current rating of the PS.
-Most circuits you are going build draw less than 100mA.
-If you are using the Boss PSA-120S, its output current is rated at 500mA.
-I assume that you are using wire somewhere around 20-24AWG.
Given the above, my opinion is that a 250-400mA fuse would protect the PS and wire (assuming 500mA output rating and 20-24AWG wire) without constantly blowing due to the current draw of your circuits.
Perhaps R.G. or PRR will review my suggetion and give us their expert opinion.