Let the printer do the imposition or if you have to handle it often, buy imposing software. The print booklet function is trash, I cannot recommend it to use.
Why do you want to make the imposition yourself?
Do you have the ADPDF9.PPD prrinter description installed? If not, you need to download it and install it before printing the booklet to postscript file. See Print booklet to post script does not work | Adobe Community
You shouldn't have to print to Postscript to get the results you're looking for, though I guess if you've got an output device that lets you re-label files to print, It's probably not that big a deal. As Peter offers, you should be able to print to PDF and get all the page geometry attributes you get printing to Postscript. And I understand using .ps file/PDF file imposition if you've got a device that lets you do 2-up printing and stitch/fold/trim the booklet inline as it's being produced.
And I truly differ with Willi when it comes to the print booklet functions within InDesign. I find they work exceptionally well.
When it comes to determining page creep, though I haven't found any software solution that works better/faster than building a mechanical 2-up folding dummy:
1) Get the number of sheets you plan to produce your booklet, using the paper stock you plan to use to produce it.
2) Fold it in half. You have just created your folding dummy.
3) Drop a ruler on the edge, and measure the distance between the end of the inside/centerspread sheet and the outside/cover sheet.
4) Enter that distance for your page creep in the Build Booklet function.
By my experience, it works every time.
I just tried the Booklet process for creep and it really sucks. No, correct that, it was not correct in form or function. The reason I want and need to do the imposition is that we are the printers. We print thousands of pages of stuff, little booklets,brochures etc, but we have never purposed ourselves to print books.
I have made a test run of 60 pages, 8.5x11 with .25" inset box and a small 1"x1" box located exact center, and the booklet moved pages diagonally for the creep once imposed.
When I printed a test imposed, no creep adjustment, 15 sheet booklet the center pages extended out to show the outer box past the page edge of the cover or outer sheet.
We use PitStop for our PDF workflow and there is an Action that does Impose, there is another action for creep, +0.0" and -0.0" which is interesting. What my test booklet shows is that once imposed I would want to -0.0" creep the center half sheets by a set distance per sheet minus the setting in subtractive formula and then do an inversely + 0.0" for the outer half to allow for all page numbers to align when bound/stapled.