I am attempting to make my first cake topper, a big 30 to stand on the top of the cake.
I've heard that you can print the letters off of the computer, and using an exacto knife, trace out the gumpaste. But I can not get it right no matter how many times I try ... Is there an easier way?? I can't find cookie cutters big enough, or I'd just do that.
I would love the topper to look something like the attached picture.
Also, I've seen pictures of cakes that have little wires with stars or flowers (I'm assuming made out of gumpaste) sticking out. I would love to make some of those... what kind of wire do you buy? Is there a trick to making those??

I do it just the way you are. Make sure your gumpaste isn't too thin and let it dry before you handle it. I cut it out, take off the leftover bits and leave it on the board I cut it on. Once dry you can smooth the edges with a very fine sandpaper.
The wires you are looking for are floral wires found in any craft shop, Walmart and often dollar stores. Failing those, a florist definitely has them. Make sure the wire is strong enough for your decoration. Something around an 18 gauge works if the attachment isn't too large.

You can also lay a sheet of acetate over the numbers and trace them out with melted chocolate, the fill them in and smooth them out with a small offset spatula. Then if you need to fix them you can just use a hot dry knife (dipped in boiling water or run under the tap the hottest it will go) so smooth out any imperfections.

I actually use a combination of fondant and gumpaste, and dry them out on cardboard.
Dries faster and is easier to cut out for me,
hope this helps!