Don’t worry! That is normal! You can’t access the SD card unless you are using a Linux machine. It is formatted in a different way that windows and mac doesn’t natively read. (It can with some helper programs)
I think you have successfully flashed, seeing as in your other thread re: the power not turning on, the light at least comes on. That is a good sign!
The next thing, re: 0.5 being buggy. I can assure you that 0.5 is leaps and bounds better, more stable, faster and cleaner than 0.4. It’s basically 0.4 with graphic drivers that actually work. It’s funny. When 0.4 first came out, everyone was nay saying it, saying to stick with 0.3. Everything has its teething problems when they first come out, and unfortunately those are the posts that remain. 0.5 is over 6 months old now, so is quite refined now.
The problems with stability people were having with 0.5 was the upgrade process. Seemingly, unless you upgraded from a clean 0.4 image, it would occasionally fail. I managed to do it fine back when it first came out, even on a heavily modified and upgraded 0.4 image. I strongly believe the majority of the problems people post about come down to user syntax error.
If you’re a beginner, then I highly recommend my custom image I made. since it comes with most things set up for you already, and most of the commonly seen mods pre installed. This way you can avoid a lot of problems with installing things, and then inevitably “breaking” the system, causing frustration with having to reformat.
The operating system is extremely customisable, but uses a very strange system that is VERY finicky. You have to learn to tame the beast! 
I would say that it is not very beginner friendly with regards to customising. That said, it is extremely satisfying once you do get it all down. I spend more time messing with the operating system than actually playing games! One day I’ll just use it as a “toy” 