You can not have multiple save files of individual towns on the same 3DS system.
Every time you save your game it generates a new, random "Save ID" and stores that ID in both the SD/Savegame and the 3DS's system memory. Trying to load a save with mismatched IDs will result in being forced to wipe the save.
This prevents two things:
- Having two towns with one copy of the game by using two SD cards.
- Reverting to an older backed up save to undo changes you aren't happy with.
http://gbatemp.net/threads/question-about-id-checks-with-3ds-and-new-leaf-save-files.349216/
I have personally tested this (having purchased a 3DS and transferring to 3DSXL- my game was cleared since the save data and the system ID did not match). Prior to this, we attempted backing up the SD data, erasing it from the SD and attempted a new save file on the same digital copy. This also resulted in the ID conflict. I have contacted Nintendo on this matter causing an inability to back up data. I am yet to hear a followup reply.
In the case of mismatched IDs, the game will load with a "corrupted data" error. This forces the system to erase any save data associated with the digital download- and any backed up save file will no longer work for AC:NL.
After going through Reggie's house, documenting all the items that he owned that I also had in my catalog, comparing the prices and doing the math, I've found out that ordering an item through the Happy Home Showcase is 1.2x more expensive.
Here are a few of the items for comparison:
Item Catalog Price HHS Price
Modern Wood Stool 1,480 1,776
Dartboard 1,520 1,824
Exotic Screen 2,250 2,700
In addition, you can only order up to 5 items in a single day. I was able to find additional sources confirming this number here and here, though it's still not stated on Nintendo's official website (which is par for the course for a lot of this game).
So if you want to order something, you'll have to pay 20% more bells, but it may be worth it for those items that you really want and/or haven't been able to find yet. Standard limitations on rare items apply here, so anything you can't order normally through your own Catalog, like the Nintendo set, Gyroids, HHA rewards, etc., you also cannot order through the HHS.
Best Answer
You are limited to having a maximum of 48 houses in the Happy Home Showcase at any one time.
If you collect more, they will replace the oldest houses, unless those houses have been saved by marking them with a heart (however, you are limited to saving a maximum of 16 houses.)