I'm studying web programming using the SitePoint books and I have few questions. Can you help me?

I would like to develop a web office suite, like Google Docs & Spreadsheets and a WebOS, like EyeOS.

1) Which format the generated data will be saved on my server? .doc/xls? .xml?

2) How can I export to .pdf or .doc/xls? Need I some plugin?

3) How can I set functions like bold, italic or autosum in the buttons? Via JavaScript?

4) How about the application's performance? What can I do in order to improve my application performace? Buy a "super server" only? Which hacks may I do in my software?

5) Witch other hints, tips, trick and links can you share with me?

Can you help me?

Best wishes,