Realistically... what would you prefer..?

Not always possible, for instance, the CPU, RAM, Graphics card and other cards all have to be installed to the motherboard, not the case (though the Graphics card is attached to the case too)
Generally, I'd advise you buy the main components like CPU, Motherboard, Graphics card and memory all at once, as you will save on shipping costs.

 

Well basically what i'm doing is buying the parts in the order that someone would normally assemble them. For instance, I have the case, and the power supply and motherboard should be getting here around the 30th, so can I assemble the PSU and mobo in the case as I get it?

 

As long as you won't be using a big CPU cooler, the PSU can go in whenever you like, but the Mobo has to go in before anything that plugs into it (i.e. RAM, Graphics card, CPU, any other cards) - that should go without saying. The longer you wait though, the less you could have paid for the stuff you bought first.

 

will they be damaged if they just sit in the case assembled? I just wanna know if it's safe to put them in the case so I won't have all this clutter in my room

 

If you don't have everything, just keep it all in the retail packaging and stick them in a larger box. All of mine fit in a box that is about 2x the size of the PC case. The only reason I say this is that it takes a while to assemble everything neatly, so there will be no way you can close your case if you just do a quick assemble. It will be hard to figure out what to do with the PSU cables unless you got a modular PSU. The only risk is really dust or something falling or spilling onto the motherboard.

You said that someone else is going to install everything for you. Installing the motherboard has to be the hardest part of building a PC for the first time, because it has the most cables to connect (from the case to motherboard). You have to get those in first otherwise it will be very frustrating to get them in with components installed (hard to maneuver with all the parts in the way). I guess the CPU cooler is tricky as well, but that is more a maneuverability issue.

 

That makes sense, I'll just keep everything in the box until I have everything at hand, and no I'll be assembling it myself