I'm a technician. In my professional opinion I think it would be worthwhile to buy the parts seperately, make sure they're all compatible, and install them yourself. It's not that tough to do a basic PC build these days. All you need is a screwdriver and a little bit of patience. Of course, if you've never done it before the motherboard manual is a big help.
The i5 processor has been a good middle of the road CPU for most computers, even some gaming computers, for a while now. It's solid ability to multitask and run at a reasonable speed will give you the speed you need without breaking the bank. If it's a budget build you could also consider AMD, however AMD processors are not worth the savings in my opinion, as you will likely face severe overheating and performance loss issues down the road which is annoying to deal with.
As for power supply, don't cheap out on this either as it affects your entire PC. I recommend Corsair 80+ Bronze PSU's. (80+ Bronze is a qualification of efficiency and reliability)
As for motherboard, I prefer ASUS, but MSI and Gigabyte are both pretty decent as well. The case doesn't really matter, as long as it's functional and meets your tastes.
As for memory, you want to get at least 8gb, preferably 12 if you are going to be gaming. I prefer Corsair, but a cheaper alternative will work.
For hard drives, I like Samsung for SSD's, and the Caviar Black series from Western Digital. Caviar Blue is a good, more affordable option at the expense of performance. Caviar green I would recommend avoiding unless you absolutely have to cut costs.
Onto video and sound. Sound is likely the least of your worries since most modern boards come with very competent sound cards already installed onto the motherboard. For video, I recommend a middle of the road GPU from nVidia. Again, I avoid AMD here at all costs. Have not had great experience with their software, as well as serious artifacting issues (severe screen tearing, discoloration and warping etc). nVidia is an industry leader, has amazing software, regular driver updates, and some of the best GPU's on the market.
If you're going to build your own or know anyone else who is willing to build this for you, it's important to keep in mind cable management. Ensuring proper and even airflow through your system will keep it healthier for a longer time and reduce overheating issues that may pop up. On the software end of things, I swear by Windows 7 and absolutely refuse to upgrade to anything else until Microsoft gets their act together. In my opinion do NOT under any circumstances upgrade to Windows 10.
I hope this has been helpful for you![]()