Ok dude, Im focusing mainly on point 3:
"I will primarily be using this cpu for internet, photoshop, and music editing. occasionally maybe film."
I do ALOT of Internet, Heavy Photoshopping (large file size/large images), and some music and video editing.
Over the past few years, I've used a variety of systems, ranging from low end budget PC's, to high end multimedia computers, and I'll tell you that for Multimedia (such as photoshop, video etc) Mac's have been the best. In my whole time using Mac's (i use them multiple times a week) I have only ever had 1 crash, 1 crash, compared to **** loads using Windows. Not only that, Image, Audio and Video editing programs run brillantly and efficently on Mac's, so for your needs, I suggest that you get the iMac, it will do what you need perfectly. Also, you can use BootCamp and install the Windows operating system, so you can use both. There is now another program that can do that too, cant remember its name...
If you cant afford the iMac, or decide against it, my next suggestion is a COMPANY made computer, that has Dual Core, 1gb of RAM, at least 200gb of hard drive space and a PCI card wireless adapter. Don't bother with custom made, at least, not for your needs, the only time you would truely need custom made is for the hardcore gamers or 3d designers. Having a company made computer has its advantages, such as warranty and tech support. When you have issues with a custom built computer and you try and get tech support, it can be absolute ****. Example: Your graphics card dies, you ring the company, they say "hey, its not our fault, its one of the other company's faulty parts conflicting", you ring the other company, and they do the same thing, blaming someone else, and it never ends.
And your better buying a computer in the budget you have set yourself, rather then buying a high end pc and upgrading it yearly, because if you constantly upgrade it will cost you more then just buying a new computer every 3 - 5 years. Computers will last as long as you take care of them, they dont just suddenly "die" after a few years.
Personally though, I would not recommend Dell for your needs. Their computers tend to be just for the standard user, not much good for multimedia users and designers.