Hi Mike,
First, you might find MIke's article helpful, particularly wrt 16 bit, here:
http://ddisoftware.com/tech/articles/september-2009-digital-photography-reality-check-308/
On the subject of 16 bit images, Qimage is an 8 bit application so any 16 bit images are converted to 8 bit; also most drivers are 8 bit as is yours for the R1800.
You'll be aware that a jpeg is a compressed file with much of the colour data removed so it, in theory, won't be as good as a tiff or raw but it will depend on the image and whther you or anyone else can see a difference in the print 

Regarding Qimage Ultimate, yes I would recommend the upgrade for several reasons, the main one for me being that all future improvements (quite a number already implemented) will be with QU only.
I print from raw in QU, it's so simple   
I find the raw conversion is excellent, especially with some of the newer, simple to use, refine features like 1-click recovery and HDR from the single raw image.
QU raw is able to use a proper icc camera profile so printing from raw can mean just one conversion and great (accurate) colours.
The new Tone Targeted Sharpening (TTS) in the editor  is a great tool making sure the right things are sharpened in an image.
There are some printing related improvements too plus an improved interface.
Of course, if you followed my simpler work flow, you may find LR to be redundant, so you have to be prepared for that 
Terry

Mike,
Terry asked me to fill in for him this morning as he is tied up with Sunday duties.

First of all I have to echo Terry's remarks about the value from purchasing Ultimate.
You already know about Qimage and it's printing and sizing and interpolating abilities.
Now learn about the Raw capabilities and the Tone Targeted Unsharp Mask, and oodles of stuff.

In answer to your specific concerns, you will receive (just ask for it when you purchase Qimage Ultimate) a Camera profile package which will include one for your camera.
Place the one for your camera, or better yet, all of them, into the folder named PROFILES.
See screen snap!
You will find it in C:\ProgramData\ddisoftware\Qimage\profiles
Will it make a difference? YES! How much of a difference? That depends on two basic things.
1) The accuracy of the colors from the camera, and 2) how critical your eye is to accuracy of color.
Many people see a big difference with the camera profile engaged, and some see no change.
Regardless, it is a step toward completing your color management loop. Camera, Monitor, Printer!

From that point on, Qimage will match the image to the profile automatically, and the image will be in the camera profile's color space.

As to the HDR and the REFINE RAW image usage, (and much more) there is a series of videos showing you hoe to do many things in Qimage Ultimate including using HDR.
Bear in mind though, that Ultimate develops raw images to perfection without using the REFINE TOOLS on 90% of your shots.
Nevertheless, I find it fun to fiddle with them anyway. 

It all depends on what you like. 

http://www.ddisoftware.com/qimage-u/learn.htm

The videos are located here.

I find all the videos fun to watch. The one for Refine and HDR is called Raw Refine, strangely enough. 

After you get acquainted with Q-Ultimate videos, feel free to pop back here and pinpoint any questions that might have arisen from the videos.

 
Hope we helped a little.
Fred