If I had a functioning brain I could be a menace to society. You are 100% correct. With an O/P of 410W you now need to find the TOTAL PARASITIC LOAD on the system. Remove the front seat and locate the battery. You need an amp clamp. These are a clamp that when put around a cable, enable you to measure the current flowing through it.
Run the bike, turn on everything, 4 ways, full headlight, brake lights, the works.
Clamp the POSITIVE cable of the battery and measure the current. Multiply that by 12 and you will have the wattage. Subtract that figure from the Alternator output (i.e.410W) and that is the power you have available. To be on the safe side, you should subtract 20%
Hope this makes sense. Apologies for being a goof