I have two side players in my town with full decorated houses. They hold a lot of QR dresses.
At first one was the runner when I needed items dropped off at a town. The other one was the island girl. She made all the money once the mayor was done for the night.
A year ago I started sending the side players out as real players. Found that it's fun not been the mayor. The mayor plays to find the mover and than the one or two players come out to play with the villagers. Christa is the young fun late night girl. Lori is the mother. They play with the villagers for awhile and than go to the island or the dream suite. They've completed most of their badges.
Found that the villagers were happier when the side player came out to play.
Other than the normal path and storage uses, it can be fun to start over with home loans and things with a side character instead of deleting the town/getting a new cartridge, especially if you've completed everything with your mayor. If you have more ideas for rooms that you can't fit in your mayor's home, side characters are great for that.
i use my side characters as pattern holders, but using their houses as restaurants, hotels, schools, etc is actually a really good idea! i might try that in the future.
My first streetpass was a person who had obviously designed their house to help streetpassers. It made me feel bad my house was full of refurbished and unorderable items. I didn't want to reorganise my house which looked perfect so I created a second character which I have filled with items to help streetpassers. Things like spotlight items, full sets, camper furniture, Gulliver furniture, and of course DLCs. Plus my collection of clocks I was keeping in the museum.
i have 2 side characters in my town. i use both of them for holding extra items and also use their house to build a public facility like 7-11 and a hotel. oh, and also for holding qr patterns as well.
I just restarted and only have one character, but my fianc? is talking about making a character in my town and I'll likely end up making a backup one to hold patterns myself. I always make my mayor basically into myself, so I like to model my secondary characters as fictional characters, celebrities, etc.
I think my next character might be modeled after American McGee's Alice, since I've been making pro design dresses from the Madness Returns game anyway...