Option 1 is the best.
I talked to a guy that implemented the
option 2 and the regulator wasn't sensitive enough to maintain the proper pressure for the demand valve, so looks like it's not a good idea. Maybe it could work with a higher quality low output (0-10 bar) pressure regulator but in general looks like those regulators are not made to be so precise with variations of demand (not like SCBA regulators which are
incredibly precise).
The original idea for such a setup was
from Joarga. I don't know if he had the same problem because he never responds to any PMs even tho he is online everyday (looks like he just CBA to answer 😂).
My other favorite setup is the EEBD, which can be implemented by getting a EEBD hood and connecting it to a Nitrogen regulator with a flow meter using an adapter.
Back in the day when EM (escMode) aka "the Canadian source" was on-line it was possible to buy entire SCBA/EEBD setups already done and ready to use.