You can use sed command to copy first 1000 lines from one file to another. You can use one of the following approaches:
$ sed -e "5000q" bpdata1.csv > bpdata2.csv$ wc -l bpdata2.csv5000 bpdata2.csv
$ sed -n "1,1000p" bpdata1.csv > file2.csv$ wc -l file2.csv1000 file2.csv