Having a massive amount of parts (430 on your rocket) creates a strain on the game. All those parts hitting other parts and exploding will take the game time, it's pretty normal for that to happen with large craft regardless of how good your frame rate is
Ye. It's better to risk only attaching some parts on your craft rather than auto-strutting and the whole thing glitching out and exploding, especially if it was preventable
Hello @Huita! Unfortunately Kerbal Space Program isn't supposed to be a state of the art graphical space simulator, (it's pretty much a game about building rockets and exploring other worlds), but there are a bunch of mods that can help you (RSS 'Real Solar System', RO 'Realism Overhaul' to name just two of them)