I'm happy to hear that there is going to be a progress finally.
However I see that technicalities in your idea are not feasible.
First, there is no way I could add entire player sprite to any scene. I can only replace individual player body segments - because in most scenes each player body segment has animation implemented as part of main animation. In some scenes it really needs to be that way because part of player body (i.e. hips) are in layer behind NPC while another part of player body (i.e. chest) is in layers above NPC. Anyway, attempt to reanimate player sprite for each scene is not reasonably feasible, specially because you can't use adobe CC for modifying any scene because it ruins AS2 scripts beyond repair.
So I need you to take current body segments from existing scenes (mark which one, not all of them are same even when it looks like) and create copies of that segments that you redraw for different species. Please keep coordinates offset (don't change drawing offset from zero point) bc it would take me hell of work to realign each drawing in sprite.
Regarding breast size, I suggest going with one size for start (i.e. breasts from Marcus scene) as number of sizes increases effort combinationary (you have to draw multiplication number of species x number of sizes).
Regarding strapon, it has two parts: straps is part of player body, already implemented in some POV scenes, we can you it as is and fit that to scenes where it's missing. The dildo is part of c0ck segment set. We don't need to do anything about that, except I can add script to remember last chosen dildo version.
C0ck set update is lesser priority. I would prefer update to be visually compatible with c0ck set in newer third person scenes. These look good enough. Also please keep current size & thickness, otherwise every size change will cause animation misalignment to vag.