Maybe Norway spruce. Closer views of foliage best. Also: any cones?

To determine how big it will be in x number of years just look at the average growth it puts on per year and extrapolate. They never stop growing, all though they can speed up or slow down some years. This looks like Picea abies, Norway spruce. Spruce usually only push new growth once a year and it is easy to see where their new growth started and stopped. It looks like the side branches grew around 6 inches and the leader most likely grew over 12 inches. =)

I thought Norway Spruces were denser. I'm about to plant 25 seedlings of them for a future screen. I have a 30 foot wide border to play with. How would you recommend arranging them?

Looks like a Norway spruce. A bit sparse -- maybe from the shade.

These will look at their best in full sun. If you have large surrounding trees that shade them for a better part of the day then they could become leggy and sparse. The more sun the better. An alternative dark green conifer that tolerates some shade and looks fantastic is Picea orientalis (Oriental spruce).

I wouldn't plant them any less than 10 feet apart. They will eventually grow into each other, shading lower branches, which could cause the foliage to thin in some locations so planting further apart would be better for the long term. After being in the ground for a few years they should start growing a foot or two per year.

I would randomly stagger the plantings since you have so many seedlings. This would also create a thicker screen, look more appealing, and create a natural look. Also if one happens to kick the bucket, a missing tree in this setting wouldn't look out of place. Happy planting!