The comment to keep it simple is Right on. But if you have time you can start googling this subject and educating your self
maybe even accomplish what you want to do. You wil probably find out that negative cooling is the as good if not better than positive. Especially if you do not have the right case for either. Dust is ievitable! You cannot stop it you can only slow it down. In fact within the next 2 weeks I need to break down one of my Computers and thoroughly Clean it. Fan filters are an option. You also would need a very special case. It would be costly and time consuming even with a lot of Knowledge.
So as was mentioned earlier Keep it simple go negative.