Yes, that's a good device. I am using it, but only problem is you have to cut your SIM card as Micro SIM. The image quality is really very cool. You can get clear picture from 24000 Feet too. Also the list scrolling is far better than the other ones.
Lumia 900 is more powerful than that but 800 is worthy enough.
Not necessary. Go to the service provider and they will exchange your sim with a micro sim. It also has a cover like thing (same as in micro sd memory cards) which can be used to convert it into the normal size sim if required.