If you don't like the white gutter, paint it with "Fusion" Plastic paint or Vinyl spray paint from the auto parts store. I prefer black, but sometimes the light bleads through, You may have to give it several coats.
When I wired this thing up, I used a 10' extension cord and cut off the female end and wired it into the fixture. You can hide too much cord but adding is rarely safe.
Marineland makes a glass canopy specifically for a 2.5, i own one, its a complete glass cover top.... try big al's thats where i got mine... you couldnt use a hang on filter or anythin with it tho without cutting the glass and thats a whole other story.....
2.5 gal is not a whole lot to keep anything. For the time, efford and possibly money you put into a hood for the 2.5 gal, you could also just go out and get a 10 gal starter kit. Those are quite cheap, and whatever you keep in your 2.5 gal will have a bit more room to swim around...