1. Your pages will get more dynamic. You'll be able to store and process stuff on your site. MySQL is basicly to store data that is submitted or so to your site. you can retrieve it and show it on your site in combination with mostly PHP.
2. there are several services out there that let you submit your sites to 1000+ of the smaller TGP's at once but the bigger ones all require hand submits. These scripts are usually pay per month.. the biggest one is
Russian Submitter last time I checked.
3. it depends on what you want it to do
If you want to build your own SE you'll probably need to spend a few years learning several coding languages