Hi Garry,
About the battery switch location, you have to found a compromise between these 2 conditions:
- the switch must be located as closed as possible of the battery (to minimise the "live part" when the switch is off)
- the switch must be located in a free and easy access area.
Regarding the polarity to be cutted, theorically, it is possible to cut either plus or minus to obtain the same result (as a cooling circuit, you can close either input or output way to stop the flow). For practical reason it is a common use to cut (and to protect by fuses) the positive wire only (to keep the negative wire as short as possible). However, if you accept to use this switch to stop your engine (like me), you have to connect the alternator wire at the upstream side (see sketch here attached) to avoid any alternator overvoltage during the stopping sequence (due to the engine inertia) and to risk to burn alternator diodes
I hope these small informations can help you.
Bernard