Your solution/concept to boot both Pasta CFW and Gateway is good. Now with BrowserHax&ThemeHax allows N3DS to run HBL without OOT/CN, plus PASTA CFW is now made to boot through HBL without the need of CN. Yes, you now can run PASTA CFW on N3DS only with just HBL through BrowserHax/ThemeHax (the first entry point is HBL, not CFW or CN/OOT cartridge). What left is use that Pasta CFW to install CN or OOT cia on to SYSNAND to be used to boot Gateway.
For those who doesn't own a Gateway card, you can do a two steps configuration similar to this making a pretty solid build. In the first step you do the tutorial to setup emunand through the CN GW launcher (this one). In the second step goes like this:
1. Format sysnand to unlink emunand
2. Reinstall themehax on sysnand (if you dont intent to use sysnand anymore go to 5)
3. Reinstall cia installer and CN on sysnand
4. Install ninjhax2 in CN sysnand
5. Move rxtools.3dsx on sd root
6. Modify themehax payload with an hex editor to boot rxtools.3dsx directly
7. Install ninjhax2 in CN emunand
With this you can start hbl offline from emunand through CN. You can run hbl the first time in sysnand through browserhax to launch Pasta. You can run hbl from pasta through CN. You can use pasta menu for nand backup things instead of GW launcher. You can install cias to sysnand with pasta. You can sysupdate sysnand with pasta, but themehax payload must be regenerated and modified again. You can install cias to emunand through rxtools. You can sysupdate emunand through rxtools. You can in fact run rxMode on sysnand (for playing virtual console games). On top of emunand you can run NTR cfw as cia if you have N3DS. Pro tip: if themehax is triggerless, you boot into emunand without doing anything in about 6-8 seconds.
