yes, but you have to get a R4I card instead of just an r4 card
All r4i cards work on 3DS. But you need to understand that the R4 cards does not work on the 3DS 3D games and only for DS games. For the first generation R4, it does not work on the cards, please refer to 'R4i cards' , 'Acekard 2i' , ' M3i zero'.
yes
This is not a simple answer... let me explain: If you have updated your DSi to version 4.0 then you CANNOT because this update will have blocked cards such as R4 etc. If you HAVE NOT updated your DSi to version 4.0 then there are two explanations. The R4 card will not work because they only work on NDS/NDSLs. However, you can use cards built for DSi like the AceCard and the DSTTI card.
yes
They are able to hold the maximum for standard SD cards, which is 2GB. SDHC cards will not work with official cards, but some clone cards have SDHC support.
It won't work because the technology is different. And IT IS LEGAL CAUSE U HAVE 2 BUY IT! There are many r4 dsi cards in the world. They support Nintendo DSi and DS console.
there are a lot of online sites to sell those r4 cards, just be careful of the R4 clone cards, there are many cards called R4 in the market, if you plan to buy a r4 card for your 3DS, i would recommend you buy r4i gold 3ds or supercard dstwo, both of them are working great on your 3ds.
no
R4 and similar cards tend to be bought online (no longer on eBay or Amazon).
No. white R4 cards are older, but should have same functionality.
nope
No, the R4 will only play Nintendo DS Games and Homebrew.