Welcome to the Apple discussions.
1) Which hard drive is recommended and how much is the cost?
See
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007605%2060000344 2%20600003341&IsNodeId=1&bop=And&Order=PRICE&PageSize=20 . Basically Western Digital drives are $90 or less, depending on size.
2) Is it worth it?
For what you've indicated you want to use the Powerbook for, yes. As eww pointed out, the 1.67Ghz systems aren't handling today's streaming video well.
3) Can I install MS Office?
Yes.
4) Can I install Final Cut pro programs?
Yes. I have Final Cut Pro 5.1.4 and it works fine. You probably know the current Final Cut Studio requires an Intel-based system.
5) What else is recommended to make the Mac current and running?
I'd install OS X 10.5.8 Leopard, which is the last operating system update available for the PowerPC systems. And I'd load it with 2GB of memory, especially if you're going to use Final Cut Pro.