well one thing you can do is to buy some scap sheet of metal similar to what you have. Goto a welding shop or where ever, it shouldnt be more then 3$ max.
Practice cutting on that if you really feel the need.
Other wise, on my window job i used a Black & Decker Jigsaw w/a Metal cutting blade. I honestly dont know how ppl can use them dremels, they break so easily, at least mine did.
As for buying a kit.. I figured hand made everything has more "novelty" to it.
Here is how i did mine:
Measured out all the stuf fon the front of my case (yes the outside, so you cut INWARDS (less mess shown outside))
Cut it and stuff, BEVELED the edges with a portable grinder tool i have (like a dremel but way better) so it makes a nice edge. bought a 2x3' peice of plexi, cut it to be 1.5" bigger on all sides of my case window i cut, and just LOADED it up with silicon.
Slabbed it on there, and it LOOKS awesome. Sanded, painted the entire case GLOSS black (including all faceplates, buttons, and legs.)
I now have a machine that is badass on the inside and outside.
Total cost: like 7$ + fun labor ($Free)
http://www.disp0sable.org/case.htm
I just noticed you have a LOT of rounded corners, depending on the quality of Jig and blades you have, and the type of metal the case is this could be easy or hard.
At the very most you'll spend time with a hand file, or a mini grinder/dremel.
Also cut it out with thick paper, or cardboard first. Put it on ur case and see how it looks, play with the design for a while.