Aluminium case are more mythic than real and efficient for the heat question. A heavy metal case do a better job against noise, but not perform better for the heat, many website have do the proof that the heat is about the same level with or without aluminium.
The first challenge in the PC Case are the cable which limit airflow circulation inside the case, and this is why the oldier flat IDE cable are not the best product if you have the choice for a modern technology. You can choose for SATA IDE which their cable are small and round or for the P-ATA you can choose alternative to flat cable with a round cable that are now available.
BTW, choose a good power supply, this is very important if you want a reliable PC.