I read that you've created 'invisible steps' for the regional aircraft - does this include the majestic dash 8?
Yes, with today's Live Update.
Also with that in mind most operators of the 737-800 etc use the front air-stairs; is there a way for me to use these with the passengers under the same premise as the regional aircraft above?
Please read Page 48 of the GSX manual, where the Embedded stair option is discussed, especially the 2nd paragraph about "Conditional Embedded Staircases". We configured the PMDG 737-800 and the P3D default L049 Constellation, to recognize the embedded stair, but only when it's used, so they can work in both ways.