Well, you've gotta total up the wattage of all your gear and the bike's systems (ignition, EFI, lighting and instruments). The gear should be pretty easy to spitball. Usually there'll be some kinda tags or markings on them giving their draw. Thing is, it may not be expressed in wattage, but rather in amperage, often expressed with an "A". Just multiply that figure by voltage, in this case 12, to get the wattage, and you should get a good idea if the Himi can handle it all.
Another quick and dirty test you might do if you already have the Himi is to plug all that gear in, fire up those driving lights, headlamp, and brake lamp, and break out a multimeter with the bike at idle. If the voltage at the battery terminals is over 13, you should be fine.