Generally speaking, all 'Not tables come without arms and then the distributor or dealers package them with a 'Not arm to provide a "package" deal. There is the Interspace arm which is often sold with the Interspace, but even more frequently I have seen the Spacearm paired with the Interspace. If you can afford the marginal extra cost it is worth the price. IMHO, you have to spend $2K or better to improve upon the Spacearm on the Interspace or Spacedeck. I have not seen the Rega arms sold in package with the Interspace personally, but a simple replacement of the stock split-ring collet ($35) will allow one to accommodate any Rega/OL arm. Again, though, unless one is going up to, say, the OL Illustrious, I would stick with the Spacearm. Even then, there are better higher-end arm choices than the Illustrious.
With respect to cartridges - If you get a 'Not arm, I would highly recommend the Shelter 501MkII, though I would NOT recommended the Denon (too stiff). Other cartridges I would recommend in that general price range are the Ortofon Kontrapunkt a (or b if you can swing it), the Goldring Eroica, Dynavector 17d, and I have recently learned that the Shure V15VxMR is a good match (though one I have not heard).
I will not disparage the Linn. I once owned one and it served me well. However, I think you will find the Interspace with a much quieter background and with a very musical presentation. Better pace and MUCH more detailed. The 'Nots, at least in my experience, have the added benefit of being extremely easy to setup, are not particularly fussy about location as long as it is high mass, and have uncanny accuracy in terms of rotational stability and consistent speed.
I continue to believe that the Interspace and Spacedeck (along with the newer Horizon) are extremely good values - proponents of alternative values in the direct drive or idler wheel table models notwithstanding.
