Sample Goals

I have a formula, n>= (Np(1-p))/(N-1)*D + p(1-p); D = ((magin of error)^2)/((z-alpha)/2)^2. However, I don’t understand how z-alpha is calculated.

My goal is the following: I have converted 500000 database records from my old legacy system to my new system. I don’t want to validate all 500000 records. Instead, I would like to validate some sample of the data. How many records should I investigate if I want a 1% or 3% or 5% margin of error?