Zerote000

My parents are by no means into tech, but they have some knowledge about it, partly because i force them to learn stuff once in a while. They have a dated but still working laptop, an iPad, and an Asus Transformer tablet. My dad uses a Samsung Galaxy S3, and my mom the mini. My dad works with a certain amount of IT at his workplace, but he's no wizard at computers (although he does know quite a bit about security and encryption utilities). He couldn't build his own PC, and before buying anything electronic he always consults me first. What really blew my mind though was the other day, i was talking to my dad about my semester project in computer science, trying to explain how the code works, and out of the freaking blue, he's like "i understand that code, i had that back when i was in school". I nearly fell out of my chair in shock, like, just, really. Here is a guy who has me set up their router when it's not working but he knows how to code a decent amount in C.....

There're always going to be trade-offs when putting together a budget surround sound system. My suggestion for you is don't blow your budget on the speakers. As a musician, audiophile and one-who-has-spent-too-much-money-on-audio-equipment, I can tell you with certainty that between a pair $100 speakers and a $400 pair there is usually very little difference. This is simply a product of the individual components not being cheap for really good speakers, and there is very little in terms of better components (tweeters especially) until you hit about $500 for a pair of speakers. In a blind listening test a friend of mine chose a $40 pair of speakers I own over the $375 pair he had just bought... he was devastated and in denial for a while, but he honestly thought the cheaper ones sounded better.
 
You are much more likely to notice better build quality in reasonably more expensive receiver that is better able to drive your speakers than a $50 price difference in the speakers. You're headed the right direction in terms of picking out used speakers, I 100% support this in most cases. However, since you're looking specifically for rear surround (which is used primarily for detailed ambiance tracks, footsteps, wind, etc.) I would suggest these: Dayton Audio B652-Air. I have there predecessor and they are an incredible value. While most speakers below $500 will have cheaper tweeters that are prone to harshness and often color the high frequencies (because they are made to emphasize explosions and dialogue), the Dayton Audio B652s are excellently balanced and fairly neutral in sound, which is great for detailed surround channels.
 
For a center channel, I would suggest the Dayton Audio CCS-33B for matched timbre and tone to the rears (this is actually more important than pairing front and center because center and rear audio channels are more similarly configured). Bic Venturi also makes good center channel speakers but they are more expensive. All the Dayton Audio speakers are wall mountable.
 
Keep in mind, I suggest these speakers because I honestly believe they are the best value under $500 per pair. However, I also suggest these speakers so that you can spend your current budget well. It's easier (and certainly more satisfying) to replace your surround speakers or center channel in the future when you have more money to spend than it is to replace your receiver. Additionally, remember that your receiver is handling all the electricity and signal going out to your speakers and should be of high quality. No company makes a cheap receiver without cutting some corners. In that light, I would recommend a Denon receiver. They are outstandingly well built, last forever, never have power handling issues, and my personal experience has been nothing short of stellar. Without have spent $150 on speakers, your receiver budget should be around $450.
 
Also, don't worry about getting a sub right now. If your front tower speakers are performing well in the low ranges, a subwoofer will only muddle the overall sound of your system.
 
As per your picks, never ever buy Bose speakers. They are way overpriced and have a very distorted sound profile that makes anything but action scenes in movies sound less than satisfying. Also, frequency range doesn't really mean anything in terms of quality. The quality of the sound you hear is in the quality of components used, not the specifications to which they were made. Monitor Audio Radius are fine speakers but won't outperform the Daytons I suggested and cost more. Dantax speakers are ok, but the build quality is not confidence-inspiring and they can sound harsh.
 
Hope this helps, sorry I wrote so much. Audio is a passion for me!