no
No. The 3DS is region locked, EU games will not work on a US 3DS.
No, 3DS games only work in a 3DS or 3DS XL.
No, 3DS games only work on the 3DS and 3DS XL as well as the 2DS
Yes
No, 3DS games will only work in a 3DS.
No, they only work on the 3DS platform. But, you can play DSi and DS games on your 3DS.
Yes, dsi games works on the 3DS also DS games work on the 3DS.
No, the 3DS is region locked.
Yes. In fact, it will have additional functionality on the 3DS and the DSi series
No, dsi games work in a 3ds, wont appear 3d though, but the dsi does not have the ability to play 3ds games.
Regular DS games from the UK will work on a 3DS from any region, including the US. It is only the 3DS games that are region locked, so a UK 3DS game would not work.
The Nintendo 3DS is backwards compatible with Nintendo DS titles, so all DS Pokemon games and subsequent 3DS Pokemon games will work on the 3DS.