You can find new and used copies of thousands and thousands of games including Final Fantasy VII Amazon.com, Gamespot, eBay
You can try this site. They have a few of those:
http://www.xboxsoftware.info/?q=Final+Fantasy+VII+game&button=GO!
You are not able to legitimately play Final Fantasy VII online. Final Fantasy VII is a single player game and was never designed with the internet in mind. You can however buy an official PC version of Final Fantasy VII.
No. You can buy every final fantasy game and tons of final fantasy gear at Amazon.com, Gamespot, eBay
There are tons of auctions and buy it nows for final fantasy 7 at Amazon.com, Gamespot, eBay
Final Fantasy VII was originally launched in PlayStation (PSX), 1997. It was then ported to Windows, 1998 and PSP, 2009. It received an Chinese unofficial port in 2005 by ShenZhen Nanjing Technologies.
There are no current plans to release a playable demo for Final Fantasy Xiii (13) on PS3 or 360 but in Japan there was a Promotional offer where you can buy Final Fantasy Vii : Advent Children on DVD / Blu Ray and get an early access demo. This however has ended.
You can buy Final Fantasy Costumes at the related link below.
I ordered my copy on ezydvd.com.au - there used to be a release date but around the 16th October I received an email from them telling me that Sony had changed the date and it is now 'unknown'... Hoping it is released here soon!
You can try searching for it on amazon or any other gaming website, or try visiting a gaming store.
It is a costume for Littlebigplanet 2 that you buy from the Playstation store for $1.99 or 5.99 as part of the LBP2 Final Fantasy VII Costume Pack.
Ioffer.com
Final Fantasy X is Teen Rated, so you would have to be at least 13
you buy them