Building oak enclosure - Advice?

[MontyP]

So I've been working on this cage, and am starting to have some questions.

From looking at the pictures, should I put any bracing on the bottom?
Would laying heat cable beneath substrate supply sufficient belly heat?
Would having half of the lid screened supply enough ventilation?

Here are the pictures of what I have so far. The cage is 5x2x2, has oak sides, front, and lid. The back and floor will be particle board. The entire inside of the cage will be lined with contact paper, and the window will be acrylic. The outside wood will be stained a golden color. This is just a rough mock-up.