Yes it can destroy ur hdd only if u dun ground ur hdd(non-metal rack)....i dun think tht config utilises air to the max efficiency.....i suggest mounting the air outlet at the back of ur casing...the air would pass by the largest hdd area plus ur mobo components on the way to the back....dust problem....it depends on ur place...like air cond/no air cond...windows open/close...distance from high traffic roads..etc.

Yes the higher the psu power...the more stuffs u can put not oni fans...go use a psu requirement calculator(easily found by google) to compute out ur max power and the power currently u using.

U need to space them out or create a diy channel tht directs air to go around the hdd b4 it goes out

yeah...it shud work better....bout dust...positive pressure inside collects lesser dust compared to negative pressure

Plus most of ur components are horizontal..therefore easier for air to flow like the pic above

Ok oso la...boleh tahan....by the way...how many hdds do u have? its best of u space them max apart and it will be cooler ade without any fans....i used to place a 3.5 in front of the hdd but now after spacing no need ade....temp hovers nicely between 35 and 40