Shell Programming and Scripting

How to make this script?

1. Write a portable bash shell script called change_password.bash that will
prompt the user for a password. Use a series of if statements to test if:

1.

The password is NOT 6 or more characters
2.

The password does not contain at least 3 consecutive letters (could be either uppercase or lowercase)
3.

The password does NOT contain any number
4.

The password does NOT contain a non-alphanumeric character (eg. Something not a letter or number.
I can take care of option 1 but have trouble making option 3,2 and 4.

#!/bin/bash
read password
echo $password | wc -m >number
number=`cat number`
if
[ $number -gt 5 ]
then
echo Password cannot contain more then 5 numbers
fi
rm number

for 3 i can only think of this but it wont work for somereason

echo $password | grep [a-zA-z]* >part3
part3=`cat part3`
if [ $part3 != $password ]
then
echo error password cannot contain numbers or special characters
fi

how do i search for consecutive letters