Back when I had gravel, it never came close to being sucked out by the gravel vac.
If you have a shop vac, that will do the job VERY quickly and easily. Otherwise, you can get a big net from the petstore for $3 and scoop it out with that. Just be sure to support the net with your other hand when removing it so that you don't break it. I preferred to remove the gravel before all the water was removed, that way I could finish draining the tank once it was barebottom, getting all the gunk out. It's not really that important that you get all the gravel out - anything left behind will eventually make it's way to the surface where it can easily be netted out.
Making the switch is intimidating, but it's not difficult. Like was said, removing everything is best, and bins or buckets are the way to go as far as storing the fish while you work. Most important thing to do is take your time and not forget anything. The fish will be fine in a bucket for however long it takes for you do do the job, so don't be worried about them and rush through it.
Honestly, the last few tanks I made the switch on I didn't remove the fish, or even turn off the filter. I netted out all the gravel, let the filters clear the water, and then poured the sand in with a pitcher. Of course I THOROUGHLY washed the sand, so I was not concerned about the water getting cloudy or the filters getting damaged. That's certainly not something I would advise someone to do - that's the kind of thing you can decide to do on your own, once you have sufficient experience and confidence.