My sister has the HQ16 sit down model with foot pedal. She does stitch in the ditch all the time. The only difference in your set up and a frame is you are moving the quilt and not the machine head. I am not real sure as to how you would use rulers with a sit down model. When my sister gets to the area she wants to do straight stitching she will mark the area with lines and then stitch over the lines.
I strongly suggest you get a pair of MACHINEGERS gloves. These are lightweight gloves that have rubberized fingertips. They grip the fabric as you are moving it. Also, the glove feels like a "support hose" for your hands and helps ease some of the stress on your wrists.
When you do get things all set up, get yourself some muslin and batting and make a quilt "sandwich" and just practice for a bit before starting on a quilt. When we set up my sister's machine we did the muslin quilt and put black thread in the bobbin and red thread in the needle. This will help you get acquainted with moving quilt to speed of the machine.
Hope this information helps and have fun with your machine.
Oh, one other VERY IMPORTANT tip for you.............BE SURE TO BREATHE!