I'm about to buy a new 3DS (the R button no longer works on my old one). Is there anything more than just removing my SD card and putting it in the new one that I need to do? For saves, profile, and other stuff.
**EDIT: See, Nintendo? You call your system New in the name and it means we can't tell if people mean a new 'old' 3DS or the actual new one. My response was written under the assumption you were getting the actual New Nintendo 3DS, so if you're not, ignore the SD card part as you have that worked out already, and yes, you can just use it on your new system. You still need to do the system transfer though. **
First and foremost, New Nintendo 3DS uses micro SD, so you won't be able to use your existing SD card directly. The new one comes with a 4GB card, same amount of storage as the SD card that came with 3DS XL and twice as large as the 2GB one that came with the OG 3DS. If your existing card is the default one that came with your system, or you bought your own card up to 4GB in size, you can simply copy the entire contents via a computer:
(1) Insert old card into computer and make a new folder somewhere called SD CARD COPY or similar, and take all the top-level folders in the SD card and copy them over.
(2) Insert new card, delete all top-level folders in it, then move the copied ones over from the computer.
(3) After you confirm the new data works fine on the new system, delete the old card data and then insert it into the old 3DS.
If you bought a card larger than 4GB and you are using more than 4GB of space on it, you'll need to buy an equivalent or larger micro SD card and do the transfer above. You'll be left with a 4GB micro SD card you don't need, but you could put that in an SD Card adapter and use it with older systems if you like or just hold onto it in case you want to sell the new system later.
As for transferring your system itself (i.e. your user profile, connected Nintendo ID and software licences), it's a separate process to the above, which just gets your downloaded games and save data onto the new system. The system itself is what holds the data that lets you play all that stuff. You will need both systems in hand.
(1) Get both systems online and update them to latest firmware (do this with your new system out of the box, just set up any old username on it as that user will be gone after the transfer anyway.)
(2) Select the system transfer option in the settings and walk through it on both systems. You basically set the old one up as source and the new one as target and it checks out all your data and will warn you of anything that won't transfer (usually save data for old DSi games I think). The transfer will start, and in my experience you should set aside 10-20 minutes. If your system has anything on it that you never play anymore and don't mind deleting, you might as well delete it beforehand to speed this part up. Personally I can't think of doing that as I want all the stuff I've had since my original 3DS, even if it just gets put in a folder and forgotten about!
(3) Once it's done your old system will be in factory fresh condition with a welcome screen asking which language to choose, so you can turn it off, insert the wiped original SD card as detailed above, and sell it safe in the knowledge the new owner will get that out of box experience.