Hi Sop, welcome.
What I would do to begin with is backup your itunes library and media files. Make a copy of the media files to another location for MC to work with so that when something goes wrong, you won't be messing with your itunes library/media files. Make sure MC does not see your itunes folder or you will end up with double entries and/or you might be modifying your original itunes files. IMHO this is your most important step, safeguard your original files and let MC deal with a copy!
MC should be able to import and play all your files, ALAC, AIFF, Wave should not be an issue. If you wish to convert, I wouldn't do that with itunes anymore, import them in MC first and convert them with MC.
Wav files do not store tags in the files, so when you import them in MC they won't have any tags. If you have organised your files on disk like \Artist\Album\Track # - Track Name.ext, you can use Library Tools to fill the properties from filenames.
I think Mc18 is stable enough for you to start out with, nevertheless you may run into issues as it is officially still beta.
Last but not least, I'm not sure how you should handle your cover art with the dummy files, maybe someone else has fancy ideas about that
.