1.) You can use the Gatewait exploit but yes, it will mean that you have to wipe Ninjhax first (why didn't GW just make a .3dsx? Idiots... They don't know what customers want).
2.) For Homebrew, if there's a .cia version available, you can install it on GW emuNAND (I think playcoin is in .cia, you're in luck).
3.) Second question answers that - you don't need HB channel if you can install a .cia.
Thanks!!