Dear Andreas,
I use DNGs in much the same way as you are proposing and for much the same reason: accurate previews and thumbnails in iMatch.
The settings I use are full-size jpeg preview and NONE of the other boxes (fast load data, lossy compression, embed original). As a bit of an Adobe captive, I'm up to date with the ACR version, but this approach has been working for me for some years, so I'm not sure the version is too important, if you aren't reaching too far back. Version 5: not sure.
Sometimes, iMatch will not generate a thumbnail image at all from a DNG, apparently at random. My workaround is to reopen that image in ACR and either make an infinitesimal change in a parameter, eg increase shadow depth by 1 and resave ("Done" button) or force a refresh of the embedded jpegs (click on black triangle at extreme RH end of the Basic toolbar and select "Update DNG previews" from the drop-down menu). If that option is greyed out, make the infinitesimal change and proceed. iMatch should then quickly pick up the new preview image.
Hope that helps,
Bruce