Minky is pretty easy to sew from my experience. Most fabrics that are very fuzzy or outright furry are quite forgiving since the texture hides little mistakes. More often than not it sheds like crazy when cut so watch out for that (and be prepared to find pieces of fluff for a long time).
Pattern sizes don't match up to the sizes of ready made clothing. In this case where you're making a skirt, which size you cut depends a little on the style of skirt. If it is fitted at the waist but loose on the hips, just cut for the waist. On any pattern, one way to do it is to cut the largest size you match then take in the other parts since that's easier than trying to make parts larger. This changes a little depending on what you're making, for example you'd pick by bust measurement for a blouse because that matters the most, and hip or waist for a skirt. What you have to consider also is how much ease (looseness for wearing or style) there is in a pattern. A lot of modern sewing patterns add way more ease than people need - you need some so you can move comfortably, but often not as much as given. So, what you'd want to do is find where on your pattern it says "finished garment measurements." Sometimes it's printed on the tissue paper, sometimes the instructions depending on brand. Compare these to your measurements. If the piece you're making is supposed to be loosely fitted, pick a size that will fit you loosely, but if it's something that is supposed to fit snug, pick one closest to your measurements then adjust.
I don't know about a thread it's been discussed in, but I did just buy a new iron so I thought I'd share my experience with that. Since you've gone through a bunch of irons, you can think about what you liked and disliked about each one. Your new one should have as many of the things you liked, and as few of the things you disliked as possible. For example, I had been using an iron with a teflon coated sole. Hated it - it felt like it was pulling fabric all the time instead of sliding over it and eventually started peeling off. So, I knew I wanted to find one with a shiny steel plate instead. Once I kind of knew what I was looking for I went through some department store websites (Sears, Target, etc.) and read the reviews on all irons in my price range that had the features I wanted. You can't go just by reviews since you don't know how these other people are using their irons, but I think it helps to get a feel for some of the problems people run into. Going to a store and actually picking the display models up is good too - it lets you feel the weight (too heavy? too light?) and press all the buttons to see if you like where they are and how they respond.
I think you can just make a tube twice the length of the elastic, slip it on over the elastic piece and sew the elastic to the tube at the ends with enough extra tube at the ends to fold over the metal clips (fold over then sew the fabric to itself around the metal end). Hope that makes sense. It would be a bit easier to explain in pictures I think.
It depends a bit on the type of undies you're making. You can use a cotton knit with a bit of stretch, like lycra or spandex, so it's mostly natural fiber (breathable) but has the stretch to stay on well. I've seen people use other knit fabrics too (like t-shirts).
I wouldn't suggest linen. From what I know, it wrinkles like mad! You could use a blend (ex. linen and cotton blend, or poly cotton) to keep the fabric breathable but easier to care for. Something like cotton gauze, lawn, or voile (which are all very light weight) could also work, or even a knit fabric so it's more form fitting and doesn't slide around on her while dancing. Have you checked out the clothing tutorials on craftster? You might find a dress pattern in there that would work for what you're doing and you wouldn't have to buy an actual pattern. Also, I'm not sure what you've looked for already but you don't need a pattern that already has the hemline like that - you can just cut a straight dress. For the blinky lights, how about magnetic ones? You could leave a little opening when you sew the daisies on to slide the magnet under or do the same with clip on lights.
I haven't made any of these patterns, but I think I can answer your non-pattern specific questions. Yes, you should cut the mock-up to your largest measurements then adjust for the ones that are smaller. Things are easier to make smaller than larger. Using a woven fabric with a pattern made for a knit can be difficult. Sometimes the clothes won't hang correctly. Patterns for knit also have less ease so watch out for that - cutting it to your size might not be enough, you might need it to be bigger and you most likely will need a zipper or buttons to get in and out (since a knit would let you just slip the clothes on but a woven usually won't). You can measure the actual pattern pieces at key points (bust, waist, hips), subtract seam allowances, and see if the finished piece will have enough ease compared to your actual measurements. Mark the dots that are on the pattern with chalk or pencil on your fabric. They're to help you match placement of things, tell you where to gather, etc. The fabric requirements seem a little high, but they're probably about right. The tiered skirt is cut with a ton of curved pieces, which uses more fabric than straight pieces would, and the top has gathering plus full sleeves. Sleeves especially eat up a lot more fabric than you'd expect. If you're not sure, you can cut out the pattern pieces before buying fabric and lay them out on the floor in a rectangle as wide as standard fabric, then measure how long the rectangle is to see how much fabric you need.
Once you have the pattern you can fold it in half then line up the fold when you cut the fabric if you want to keep the circle continuous. As long as you have the pattern made up with correct measurements, you can cut it up into as many segments as you want. Just make a note of how many segments are needed for the whole skirt - for example, if I drew out the pattern and cut it up into 4 pieces, keeping only 1/4 to use when cutting fabric, I would make a note to cut the piece out 4 times (plus seam allowance) for a 3/4 circle skirt. If you're having trouble following her directions for the pattern itself, I suggest trying it. It might make more sense when you're actually doing the math and drawing it out.