It should work without damaging it. When having it in hands, you can unscrew the black retainer ring (with a knife blade or something).
When the retainer ring is removed, the two small lenses and the spacer ring between them should fall out. If not, gently push something through the front end.
No, the picture you are referring to is from a build with Brian's (@Bulldog44) scope with hollowed core and shows two casted resin pieces holding the small lens in place. This is slightly different to what you are building.
According to my research back then, the two small lenses with spacer ring are used to compensate the pillow- and barrel-distorsion (see the graphic from my earlier comment), which is useful for real telescopes. In our resin builds we do not get them to work like that (believe me, I tried hard). We just want both scope ends to look real. From that point of view, it is absolutely up to you if you want to install just one small lens, or both of them with that spacer ring. As for the orientation, I would always install the domed side facing the outside. Real telescopes have it that way and you want yours to look real.
Not sure on this one, as it never had any impact on my builds. Give it a try and play with the parts you have, try various combinations and check if one changes anything...