Turn 3d helmet model to printable STL file

I have ironman movie helmet 3d model that needs to be turned into a printable 3d model.

WHAT YOU NEED TO DO:

1. Make model parts double sided with thickness.
2. Make all parts logiacally fit. Connecting parts would be a big plus.
3. Preserve exact supplied model outher shape.
4. Keep geometry as clean as possible.

Currently all parts are one sided (inner faces deleted). Some parts are intersecting and dont logically fit. I can supply 3d files for you to check before starting the project.
This helmet will be 3d printed and worn.

I've attached how model looks currently and reference. Reference should not be copied exactly but used as a guide since it was done by somebody else.

Please let me know how long it will take you to make this model printable when you submit a proposal.

Thank you