You ask some good questions, and I'll just pick and choose the ones I want to respond to. Maybe not the most important ones. Most people who buy three piece bows never take them apart. They just like the balance of a little more weight in the riser. If you knew which arrows you wanted to shoot, the best bargain is high priced carbon arrows, because they don't bend or break nearly as easily as wood or aluminum arrows. But they are just as easy to lose. And some people love to shoot wood arrows, so that's the end of the subject as far as they are concerned. But it takes some experimentation to decide which arrows you want to shoot, and you could waste your money if you buy carbon arrows too soon. It's fairly easy to match up aluminum arrows with a bow, and you should probably just accept that you will bend or break most of your first dozen arrows pretty soon anyway, so get some aluminum arrows to get started (unless you love wood). Which brings up the subject of repairing arrows. I shoot just about every morning, and it's a rare morning that I don't have at least one arrow that needs to be repaired, so fletching jigs and spare nocks are probably in your future too.
The three bow companies you mention are fine companies, but probably 95% of our members shoot bows made by another 25-50 bowyers who specialize in traditional bows, such as the ones you see advertising at the top of each page.
50# is okay. 45# would probably be better for learning, and you could also hunt with it. Nobody stops with one bow anyway.