You can find a list of potential entry points here:
http://smealum.github.io/3ds/ , select the one you own then follow through the link to get more details, note that many of them don't work on 11.1 (pretty much none of the "Easy" entrypoints (not requiring an additional game) work on 11.1) but if you own one of the things that works you can go from there. There's also Steelhax but that's no good to you , since its an eshop download and you need another entry point to start it (so you can use it after you do a system transfer by setting it up first, but it's no good for dumping saves on the N3DS).
Yes, the NNID from the O3DS will be transferred when you do the transer (and you can't transfer back since its N3DS to O3DS which is a no go) but if you don't mind losing the stuff from your O3DS you can just system format after you've got the CFW setup and then put in your N3DS NNID again (the CFW stuff isn't affected by NNID / System Formats post-install).