Also can anyone tell me how the 3DS Music Player works out? Is the volume greater than the one in DSi?

As far as DS games go:

Racing Games: Mario Kart DS
RPGs: The World Ends With You, Lunar Knights, Rune Factory (well RPG/farming sim)
Music Games: Elite Beat Agents
Platformers: NSMB is a pretty obvious one

1. Mario & Luigi: Bowser's Inside Story, Chrono Trigger, Dragon Quest IV/V/VI/IX, Final Fantasy IV, The World Ends With You, Radiant Historia, Golden Sun: Dark Dawn, Infinite Space, Nostalgia, Inazuma Eleven, Anno 1701: Dawn of Discovery, Phoenix Wright series, Professor Layton series, Broken Sword: Shadow of the Templar, 999, Kirby's Canvas Curse, Might & Magic: Clash of Heroes, Puzzle Quest, Tetris DS, Advance Wars: Dual Stirke, Age of Empires, Ghost Trick, Last Window, Hotel Dusk, Scribblenauts, Clubhouse Games, Soul Bubbles, The Legend of Zelda: Phantom Hourglass/Spirit Tracks.

No, I haven't listed all my DS games, just the favourites.

Also highly recommendable even though I suck at them: Castlevania games.

You get pretty screwed over with White Forest, yeah. I went with White for pattern purposes (i've always had the second of two titles), but i'd recommend Black

As for the "DS noob" question, we've got this http://gamrconnect.vgchartz.com/thread.php?id=36367

As for saving coins, if you don't like anything you see in current prizes, you can wait, but coins will expire two years after they're registered, so eventually you're forced to use it or lose it, but it takes a while.

If you reach platinum status Nintendo is going to ship you some gift (2009 was Mario's cap; 2010 a Mario Bros figure and 2011 a Punch-out Wiiware where you had to beat Doc Louis)

Yah Club Nintendo is a program that rewards consumers for purchasing Nintendo products.

If you reach Platinum status then Nintendo will mail you a promotional item. In the past a Mario Cap, Punch-out DLC and a Mario Statue were all given out.

Get Gold status and you will likely get a Nintendo themed calendar.

As for spending your coins, Nintendo offers new rewards every now and then and takes others off. So if you see something you like buy it if you don't then save your coins. Nintendo of Europe and Nintendo Japan have given out some pretty sweet promotional items in the past.

I'll answer 1:

Despite it being my favourite DS game, I would not get Mario Kart DS and wait for the 3DS version in a couple of months. The games that I would recommend are: The World Ends With You, Final Fantasy Tactics A2, the 2 DS Zelda games, all the Prof Layton games, both Advance Wars, all Dragon Quest, the 1st Inazuma 11 (and the others if/when they get localised), Elite Beat Agents and probably loads more I've forgotten.

DQMJ if you're want something pokemon-but-not-pokemon. It's dirt cheap now.
*waiting for DQMJ2 to get over to NA*

It's based on the number of coins you earn within 1 year. You have to register 600 coins (it seems) during 1 year to gain platinum status for that year. Even if you use those coins on prizes, they will still count towards your status.
E.g. if you registered 650 coins until last month and then buy an item for 600 coins, your balance will be 50 coins (650-600), but you will still have platinum status.

I noticed how no one has mentioned GTA: Chinatown Wars for DS. I'm playing it just in these days. It's more similar to 2D gtas, like GTA and GTA2 It's great.