This is a very weird question.
No you can't use the original R4 on the DSI, but there is something called R4i that's supposed to work on the DSI.
Only micro SD cards work with R4i.
yes you can but you need to download a software called r4i update
Typically R4i cards are only bought online - but I wouldn't buy an Ri gold card. It's a fake card (the original R4i is red in colour). Most flash cards are made in china, including the r4i gold card. you can buy the latest version - r4i gold 3ds card online. It usually cost 2 weeks to delivery to you. As before said, the r4i gold 3ds is not the best r4i card. Maybe, the r4i sdhc 3ds is better.
The R4i Gold is a fake card released to try and take advantage of the R4i selling so well worldwide. R4i sdhc and r4i gold card are different flashcard. they are similar in functions. But different in package. they use difference kernel. Both of them are popular in Players currently.
How much is v20 12k worth
If you updated the DSi, the new update may prevent you to use the R4i
If you use it to play Roms, it is.
Yes.
R4i is illegal b/c r4i is a device for pirated games which is stealing from the companies that created the games.EDIT: The R4i was legal, because you could use it in legal fashions. However, selling, advertising or importing R4i and all similar cards is now illegal in the UK. This is a recent ruling, subject to a pending appeal.
of course, new r4i v1.6 kernel can work on all below version of r4i card, including r4i v1.4 kernel.
Download newer firmware (sometime named kernel) from your R4i's website and install it on your microsd. Make sure to download it from the correct website. There are many R4i model and they don't all use the same firmware, so use the one stated on your R4i's label. Before deleting anything from you microsd, I strongly recommend to back it up on your computer.