Chibiusa and Hotaru have a very special and intimate relationship, and that's what we're here to discuss. First let me state my opinions on the matter clearly and cleanly and then I can get to exactly why I think the way that I think.
Hotaru is Chibiusa's closest friend in the entire world, past and present with the possible exception of Diana, but we'll get to that later. Chibiusa and Hotaru are not in love. Chibiusa loves Hotaru and Hotaru loves Chibiusa, but they are not in love. Hotaru and Chibiusa are so intrinsically tied together that Hotaru eventually takes up a post within Chibiusa's court of Asteroid senshi and remains by her side faithfully once her duties to the Queen are dispersed.
Throughout both the anime and the manga of Sailormoon there is never the slightest mention of Chibiusa and Hotaru having a romantic relationship. You can't "read it between the lines" the way you can with Michiru and Haruka (in my opinion you don't need to read any of that between the lines. It's pretty plainly stated). There is only one comment that might suggest something of that nature in all of the anime or the manga, and it is intended as a joke. Chibiusa tells Usagi in volume sixteen of the manga that it's fine for her to hold hands with Hotaru because Usagi and Mamo-chan hold hands all the time. This comment pisses Usagi off. I believe that Chibiusa means to say that Usagi and Mamoru are just friends, and not that she and Hotaru are involved. That would also explain why Usagi gets angry at the comment.
To further discount the idea that Chibiusa and Hotaru are involved is the plain and simple fact that both the manga and the anime heap lots of evidence on the table for Elios and Chibiusa. Chibiusa never has the feelings she has while she's sorting through her relationship with Elios while dealing with Hotaru and that should tell you something.
I should also say that I have nothing against Hotaru/Chibiusa shoujo ai, should it be written well and intelligently and take all things into consideration. You can make a case for it developing, it's just that neither the anime or manga presents any evidence for it other than their close friendship.
As to the idea that Sailor Saturn will stay close to Chibimoon even after Chibimoon gets her own court, that can be easily read between the lines. In volume fifteen of the manga, it is Saturn who retrieves the balls that contains the souls of the Amazon Quartet and it is Saturn who asks the newly ascended Neo Queen for power to revive them. When all the other senshi ascend into princess form for the coronation of the King and Neo Queen, Chibimoon and Saturn both remain in their fuku, watching solemnly.
As a final bit of evidence, there is one particular artbook image which features the Amazon Quartet, Chibimoon, and Saturn all together, although the other lunar senshi are grouped separately in a different picture. It is also easy to imagine the youngest of the senshi gravitating to this younger team.