First, congrats on the bike! I have a 7.5FX that is a blast to ride, you'll love it.

Perhaps using the smaller clamp or spacer the PBSF comes with, you should be able to put the light on the very rear. It will be mounted 'sideways', but should work. You may also be able to mount it on the vertical support of the rack.Most racks comes with hardware or a spot for attaching a light or reflector, are you sure you arent missing something?

Note that the PBSF has a habit of shaking apart, this is supposedly fixed in later versions including the Stealth, but just in case consider a bit of tape and/or an ORing to hold the 2 parts together. Otherwise they are great. Another fun toy is the WF-501B which can be 'upgraded' with sku.26345 for strobing.

I dunno anything about the Tank flashlight, but there are brighter ones for about the same money; also it wont run too long on AAs, so use 14500 cells. I have several Ultrafire Q3s that work well. This size light is often used on the helmet to augment a 'real' light as they arent bright enough to 'see', do not run long and have a very narrow beam. I would not use an AA/14500 light as the sole means to be seen.

For travelling unlit roads at night, you should have more light than those give. The P7 you mentioned is a fave. Many people also like the TR801 which is very bright. These are more comparable to a 'real' bike light except for runtime and beam/throw. Considering the price you can get 2 and have a fair amount of light to see/be seen and not be depending one one light source.

I have that 9LED taillight and they are great. Very bright and lots of blink patterns. I havent had it long enough to comment on durability, but it looks no worse than any other light.