Use grep -n to get the line number of a match.
I don’t think there’s a way to get grep to start on a certain line number. For that, use sed. For example, to start at line 10 and print the line number and line for matching lines, use:
sed -n '10,$ { /regex/ { =; p; } }' file
To get only the line numbers, you could use
grep -n 'regex' | sed 's/^\([0-9]\+\):.*$/\1/'
Or you could simply use sed:
sed -n '/regex/=' file
Combining the two sed commands, you get:
sed -n '10,$ { /regex/= }' file