Starting Apache and MySQL will take some additional time, but other than that if you give these services nothing to do they won’t impact your system performance (they won’t eat much CPU in idle; and any memory they need goes to swap). However, and you can probably do this through the GUI as well, here goes with a few commands to switch them to manual.
List all the services on your machine:
Look for the apache and mysql service name. Once you have the correct name for the apache and mysql service from that list, switch each service to manual with the following command (replace <servicename>, including the angle brackets, with the service name from the list):
echo manual | sudo tee -a /etc/init/<servicename>.override
After reboot those services will not start automatically. You can start them with:
sudo initctl start <servicename>