>Is it absolutely necessary to perform my "PRE" White Balance test with the filter off (I read it has a blue tint but...)
If you are going to use the filter when you shoot, then Pre-set the WB with the filter On. If you are going to shoot without the filter, then Pre-set the WB with the filter Off.
>Is it okay to not use a lens hood to do the "PRE" test? (I don't have one and should I get one and why?
Yes! I use an Expodisc to pre-set the WB and a hood gets in the way. If you are using a gray card I would use a hood on the lens. I would recommend using a lens hood all the time. I do. 1. A lens hood will reduce the possibility of flare and ghosting. 2. A lens hood adds a layer of protection between the front element of the lens and your surroundings. Good Luck and Enjoy your Nikons!