Solutions for problems in linux terminal

Hello i have 4 questions :
1- i have 10+ files with different permissions
if the group of users has less permissions than other users then i remove those permissions for the other users to match the group users
for example if i have -rwx---r-- then i am gonna make it -rwx------

if i have -rwxr--r-- it stays the same
if i have -rwxr----- it stays the same
what is the command for this one (one command , no pipes)

2- i have a file that has words
i want to count the words that have more than 10 characters
one command

3- i have log files that end with .err .sol
separated in multiple folders
i want to get them all in one folder in one command no pipes
4- i have a file that has multiple words most of them are repeated
i want to make another file that has only the repeated words also one command

Thank you so much for considering to help