So I'm building my first PC, i'd say im a gaming enthusiast, and i was wondering if i really will need crossfire for my AMD 7870? (Will be playing in 1024 X 768) Because i could save some money buying a non-crossfire mobo and a smaller power supply.
Many people don't like to run multi GPU's because you end up with more micro stuttering and stuff. It's hard to say for sure until you try it. I don't really care for it myself but you never know if you'll come across a 7870 for real cheap.
Unless you plan on getting a much, much higher resolution display, there is no point in even considering Crossfire. Your single 7870 is already massively overkill for such a low resolution. For most of your games you are probably CPU bound when it comes to performance if you are only running them at 1024x768.
I'd say pick up a 1080p monitor with your build, it will look much nicer, and actually allow you to use your 7870 at its full potential.
You will definitely not need crossfire because a 7870 @1024x768 will be more than enough to max out the majority of games(depending on your other specs of course). I'd personally recommend buying something that can be upgraded later i.e. the mobo with the extra slot, but crossfire isn't that advantageous. I just crossfired my 6870 with another one and it's hard to see the advantages, but I'll live till I can upgrade.
I didn't even look at his resolution, I would use that money from a second card and buy a monitor. And I don't hardly care about monitors myself, so I would just buy one like this: http://www.newegg.com/Product/Product.aspx?Item=N82E168... I like Dell accessories, they've always worked very well for me in the past, I just recently replaced my dell keyboard that I have been using for close to 10 years.