Clean Part loaded - how to bring the Enviroment (Dplanes, Relations etc.) on it?

Modelcheck is the easiest way to do this from the user standpoint. But setting up modelcheck to do this would be a project and would take some time.

As a user, I would make  mapkeys to semi-automate the process of adding datums, relations, parameters.

I would also ask, Why do you have parts with none of these things in them? Are you using start parts? Are you importing models into empty parts instead of importing them in to a file with your start part features?  I do understand there are reasons sometimes but avoiding having to do the extra work would be the ideal solution.

Creating and using mapkeys is your best bet.  Many of the needed items can be imported, by mapkey, from a file created from a good model (parameters, detail options, relations, layers, etc.).  Others will need to be created, by mapkey, with some user intervention possible with a pause (default datums, layer rules, orientations, etc.).

I have a mapkey that we use to add parameters to files without the required company parameters. Very simple to update and add your own parameter names, if the parameter is designated to Windchill and even an initial value if needed.

Creating a mapkey to add datums and coordinate systems is easy. The drawback is that in my case, ModelCheck will flag a warning that these are NOT the first 4 features in the model.

Alternate suggestion is to create a new file and then import your existing model into this empty file to get the right datums and parameters.

Depending on the number of files... I would make a mapkey to open a proper new start part with the setup you want and copy the model(s) into new parts. Then do the part number shuffle onto the new fixed version and import to windchill as modified. Squeaky clean new parts. 

I do fixes like this from time to time on old or usually noobed up models. Also for replacing files with weird unfixable corruption, except I usually have to recreate all geom for those yikes.