Sprouts should be about an inch. If a little more than that, it’s not problem. You can get them to sprout faster if you bring them out into a room with medium light. Keep the temps around 60 to 70 degrees. Regular humidity in Texas this time of the year should be ok in the bathroom or kitchen.
It’ll just take about 1 - 3 weeks, and they should be ready to plant. Remember you want 2 or three sprouted eyes per plant. I am not that familiar with fingerlings, but regular potatoes are cut to about the size of 1/2 a large chicken egg.
OK, will bring potatoes out for medium light. I keep house about 72. I read about Fingerlings and most plant the whole potato so I will.