Hi Eszajer and
OS, monitor, keyboard and mouse is already taken care of.
What about speakers? As far as your OS, understand only full "boxed" Retail
licenses can be transferred to new computers. It is illegal to use an OEM license that came with or was purchased for another computer on a new computer. If the disk says OEM/System Builder, Upgrade, Academic Edition, or "For Distribution with a new PC only", then it is not
transferable to a new PC (or upgraded motherboard) under any circumstances. These OEM licenses are inextricably tied to the "original equipment". If that is the case, I recommend 64-bit Windows 7 or one of the many free Linux alternatives. Just ensure it is 64-bit since you have selected 8Gb of RAM.
If you are wondering about a specific product, enter the model number and the word "review" in your favorite search engine, then look for hardware review sites. Beware of sites that simply post what the maker's marketing team posted. You want real reviews. Also beware of user reviews at sites like Newegg. Happy users don't complain for one, and one or two bad reviews out of 1000s sold is nothing. I only pay attention to user reviews if many buyers complain about the exact same problem - indicating a trend.