One of the simplist ideas to improve airflow is to tidy the wires away, another is to use rounded IDE cables like this click here you can get rounded cables for the floppy as well. Basically anything you can do to clear the airspace and therefore increase airflow is good.
Not sure about the side fan sucking air in. I have a similar setup but have the side fan extracting air, front sucking cool air in and rear sucking the warm air out of the case, perhaps the way you have it is better I don't know. I can only say that my PC is stable as it stands. Generally if you have 2 fans, 1 at the front and 1 at the rear the rule is 1 in and 1 out, usually in at the front and out at the back. What a side fan does to the airflow and which way its best to have it I'm not certain about I can only say what I have.