Very interesting FFF. Personally I found flying approaches on a simulator good practise for gaining familiarity with a particular approach, but not for the overall nature of flying an instrument approach. Not sure how clear that is - what I mean is that if I knew I'd subsequently be flying a particular approach in real life I'd do it a few times on the sim as this would help me later when visualising what was going on when I couldn't actually see anything. But it didn't help me learn to prioritize, or remember to do certain checks, or start the stopwatch, or make radio calls etc. I think this is because these things don't have any consequence in the comfort of your living room or your study. As such, using something like RANT is perhaps better for this kind of practise, because then you concentrate purely on the procedure.
As another personal observation, I don't think studying loads of approach plates is a good idea. When you become more experienced you get better at picking up the salient details, but in the early stages of learning I think it is helpful to just concentrate on as few key items (outbound track, DME at which to commence the turn, inbound track, descent points, etc.). as you can get away with. Otherwise it all gets away from you and, as you've found, once that happens it is harder to get back on top of it.
But don't get disheartened. It is all too easy to get fixated on something and it screws up everything else. I remember my instructor starting to raise his voice when he had asked me to go around and I was concentrating so hard on the glideslope. He ended up saying "You are diving at the runway", which when I looked up I realised was true. Another time when I was doing a go-around I called ATC to tell them but was still thinking so hard about the final stages of the approach that I didn't let go of the PTT after making the radio call. I just sat there, frozen with my finger pushed down. Turns out it was only for a couple of seconds but it seemed like ages. And then, after a while, all that just stopped happening and I started to relax and enjoy it.