Not much too add other than templates and routers work great. I started cutting my wood last weekend and basically got one side done and then used that as a template for my router; Worked great.
I can't tell if it my lack skill or my jigsaw (or both) but I also have a heck of a time getting it to not wander. So, I tend to not use it very much. Not sure what is available in your area, but maybe it would be worth it to buy or rent a circular saw and just use the jig saw to complete any cuts/spots that the circular saw cannot complete..? I find that if I clamp a "fence" to what I'm cutting I can get very good results with a circular saw, for straight cuts of course.

Good luck with the build!