The “little space” was above 60 years, counting from the second year of Darius Ezra 4:24, or about 80 years, counting from the first year of Cyrus Ezra 1:1. This does not seem to Ezra much in the “lifetime” of a nation.
A remnant to escape - Rather, “a remnant that has escaped.” The “remnant” is the new community that has returned from the captivity.
A nail - Compare the marginal note and reference. The metaphor is probably drawn from a tent-pin, which is driven into the earth to make the tent firm and secure.