250 would be fine. I used a 250w HPS in a cabinet that was 18"x24"x52" for my first grow. This is a final pic of my first plant: Attachment 283875

400 is better without too much extra heat. Purchase a few PC fans and use those, they work great to vent the hot air. A small oscillating fan to aid with fresh air circulation and you should be fine. A t5 will work fine for veg.

Let us know what your room dimensions are and I can give you a better idea of how to set it up.