How to move Aperture Application back to computer, but keep Library on External HD?

Question

Many thanks in advance for your attention.
1. As my Aperture Library started out of the gate large, I began by putting both the Aperture Application and all of the Library on an External Hard Drive.
2. How do I move the Aperture Application back to my computer, but leave all the Library (and its photos, contents, etc.) on the External Hard Drive?
3. I tried opening a new Aperture Library on my computer and then attached my External Hard Drive.  I tried clicking that I wanted to keep all the data on the Eternal Hard Drive (presumably this would just transfer the Reference files to my computer - but leave the 100s of GB of photos and data on the External Hard Drive). But the Import button remains greyed out. It is like the Aperture Application on my computer sees another Aperture Application and Library on the External Hard Drive. One Library is open (on computer), so it can't access photos in 2nd Library - (External Drive). But if I open up External Drive Library, then I can't import in the direction I want.
4. I don't want to import One Project. I am trying to now have my Aperture App and Reference files on computer, while keeping all my photos, etc. on External drive.
5. One more question as I have read and heard it both ways. Some people say - One Aperture Library for all photos is the best way. That is the point of it. To organize all your photos.
6. Others say - One library is absurd. As it grows and grows, it slows down and gets sluggish. Better to have multiple (smaller) libraries.

Answer 1

Thanks for this link as well.
This person seems to want to illustrate that you can have multiple Libraries, which you can.  The first example given is a good one: one Library for professional work (I was paid to make these, and I sell them), and one Library for, as the author states, "snapshots of family and friends".  The second example is suspect.  That is the author's Library for his Aikido club.  This seems set up simply so that he can show a third Library.  The Library does no appear to be used much, and is very small.  There is no reason such a Library shouldn't be either in his Professional Library (I get paid to take shots of my Aikido club) or in his personal Library (my Aikido friends).
I put both this person and the other person to whose video you linked in the category of helpful people who have knowledge but not much experience.  (And let me here acknowledge that I tend to overstate my case: I'm happy to have my experience improved -- but I didn't see anything in either citation that did that.)
A year ago I stated my general rules for creating Libraries.  I stick by them today:
My rules-of-thumb are:
•  One Library for each photographer or group of functionally identical photographers (a company that shoots weddings, for example) when the author/copyright-holder of the image is important.
•  Separate Libraries for "authorless" images of a specific category (I keep a Library of paintings and drawings; who made the photographs is of no interest).
•  Separate Libraries for items which need to be handled securely (medical documentation, for example)