I can't stress enough how the pros and cons of everything from the case down to the cooling system has me in complete fear
Welcome to building computers! And I completely understand your fears. Like everything else in life, there are no guarantees.
Reading reviews from MaxPC, Anandtech, et al. is great...BUT they can't review every piece of hardware. Personally, I do use reviews on Newegg and Amazon as a resource, but you have to evaluate the legitimacy of the reviews:
"DOA. Never buy again!!!" is not a good review
"Pros: Everything Cons: Nothing" is not a good review either
Try to find reviews that provide details. You wouldn't believe how often I've found troubleshooting validation or support by reading reviews. And read both good and bad. Get a sample.
In general, I look at the reviews as a whole. If 75% of the reviews are 4 & 5s, chances are it's a pretty good product. I would even go as low as 70%. If it's a 50/50 split (half 5 star, half 1 star), that's harder but to LatiosXT's point, more people will write a poor review than a good one.
As for the HDD, there are two main reasons to use a primary drive and a data drive. First, since SSDs are so expensive, you can use a smaller SSD (I recommend 250GB) to house your OS, games and applications, but then use your HDD to house your files (pictures, documents, even less used applications). Second, if your primary drive fails you can re-install your OS and still have all your data.
Hope this helps.