1. When I sandwich it, do I baste or use safety pins?
You can baste with thread, glue, basting spray or safety pins. If using safety pins, I'd suggest the curved ones (JAF or HL sell them). I prefer pin basting & place my pins a fist-width apart. I baste from the center out, in quadrants.
2. I don't have a large table or access to one and I don't even know how or where I can sandwich it.
I baste on the floor.
3. Quilt-in-the-ditch would probably look best, but do I have to quilt every ditch? Some are just an inch apart.
You can choose whether to quilt all the ditches ... just realize that any ditches/seams that are not quilted will puff up very slightly along the center of the seam. If it's not a show quilt, it's not really a problem.
4. The batting package says it can be quilted 10" apart, is that true? It seems like a lot.
10" for anything meant to be a utility quilt is too far apart, in my opinion. I almost never quilt farther apart than 2" in order to ensure sturdiness & longevity of the fabric and stitching. The batting instructions are only in regards to the point at which the batting starts to wear/bunch/develop issues. Your batting will be fine if you only quilt every 10", but it is really hard on the fabric. If you want to be sure your quilt will be problem-free for years to come, I'd quilt it much closer than 10". If you only plan to use the quilt for a couple years, or don't mind the occasional little fixes, 10" is fine.
5. Do you think I have time to do it before Christmas? The backing and binding are all cut and pieced together.
Potentially. I've quilted quilts in that amount of time, but with the time to practice & downtime during the Thanksgiving holiday/holiday shopping/winter parties ... if you're also working full-time (that includes parenting), it might be a bit of a time crunch to baste, quilt & hand bind all before Christmas. Still, I think it's worth it to give it a try as long as you'll feel okay in the event it takes a bit longer (I know I never seem to get family quilts done in time for the actual holiday/birthday for which they were intended ... something always comes up -- usually I wear myself down with late night quilting even if I have to get up for work the next day & then end up getting sick and being unable to quilt for a week or so -- maybe one of these years I'll learn 
).
6. Any suggestions about practicing before starting?
Use 50wt/2ply or 60wt/3ply thread that matches or is a shade greyer than your primary background fabric. If your walking foot comes with different soles (like Bernina), try out the different options. I like the open-toed best on my Bernina & the closed toe best on my Singer. I've never been able to get the hang of those ones with the ditch guide, but maybe that's because I use dense, high-loft batting (Warm & Plush). Also, note that "Quilting Needles" are actually for Free Motion work; for SID you're better off with either a Microtex or possibly a Top Stitch.
Edit -- Oh, and 2 more things ... (1) be sure to watch a good video on how to properly baste a quilt -- the biggest thing that got me was pulling the back too tight before taping it to the floor and (2) most importantly (can't believe I forgot this!): HAVE FUN! Quilting is super addicting & once you start you'll want to quilt all your quilts! 