Looks like you got a few pretty sharp edges on there.
If you insist on using aluminum (I think you would be happier in the long run with plastic) I would round down those edges a touch. Aluminum, believe it or not, is a nasty metal with which to get cut. Some studies I read about in a medical microbiology course stated that wounds caused by aluminum can be more prone to nasty biological infection than wounds caused by rusty iron, even accounting for tetanus bacillus.
Plus, depending on what gauge you used, the aluminum can be easily bent and ruin the shape you worked hard to make in the first place.
Call some local sign making shops and ask them if the have any Sintra scraps that they are throwing out. This can be easily formed using a heat gun or with some patience even a hairdryer. Then run it under some cold water and "voila"...it retains the shape.
