sinking isnt an idicator of a good seed. I have had floating seeds grow as well as seeds that sank in 12 hours.
The reason that you soak them in water is to introduce water, which starts the germination process. It isnt necessary, you can introduce water via soil as well, or paper towel etc...
Soaking them in water, then wrapping them in a moist paper towel, then planting them in properly moistened soil is redundant but as long as you dont let the seed open and stay out of its final home for too long, you can do whatever youd like.
I have never done the sandpaper thing. My seeds sprout in a few days. Never felt the need to. If you are in that much of a hurry that youd sand your seeds if it might knock a day off that time, its going to be a looooong grow.