There is a lot of tremendous advice here! Seems like the guy at the third hobby store steered you best and got you started on the right track.
In addition to what you got from him, I would HIGHLY recommend a hobby knife, as mentioned before. I got a long fine for a long time without any sprue cutters - just cut the part off the sprue with the knife. You'll notice that between the sprue and the part is a little tab - I make the first cut on the end of the tab adjacent to the sprue, then when the part is separated form the sprue, clean it with my knife and sandpaper; this makes a nice clean cut without special tools.
Other than that - well, just take your time. I wouldn't bother sanding a lot on this model, or puttying at all. There should be a minimum of mold lines on the body, which should clean it mostly up, and adding "bite" for the primer isn't that necessary (that's what primer's for!) and adding "bite" on the primer for the paint isn't that necessary either (that's what primer's for!); but feel free to do what works best for you. Just try not to over complicate things!
Since painting the body is, for most people, the hardest part to get right, don't freak out if it's not perfect. And here is a great tutorial with pics and a video (which I found astonishing and surprisingly informative):
http://www.tamiya.com/english/scale/beginner2/2.htm
And more info about other aspects:
http://www.tamiya.com/english/scale/beginner2/index.htm
And always keep in mind that if you enjoy this, you'll have plenty of time to accumulate tools and paints. Just get started and have fun! There's really no right or wrong way to do it. If taking only a couple days and leaving out a lot of parts is fun for you, then you're doing it right!