Here's my take on it, for what it's worth:
1) OFFSET G is a far better choice both ergonomically and mechanically. It has no effect on sound. After decades of being bound to the in-line configuration which was originally chosen for reasons of manufacturing cost, the prejudice against offset G is declining. I would not recommend anyone except experienced players who want a specific instrument for its particular characteristics buy an inline G flute. Definitely not a high school player.
2) Low C or B is largely irrelevant by itself, but in better grade flutes in the US, the low B instruments are more likely to be in stock. Personally I prefer the low C as I think the third octave responds better.
3) Open or closed holes is a long standing argument. Personally I believe most flute players are better served with a closed hole instrument, but the prejudice is so strong that you probably ought to get open hole. Anyway, open holes can always be plugged. I very seriously doubt that tone hole location is selected especially for open vs. closed holes except on the most expensive flutes. I play an open hole instrument with the holes plugged.
4) I have not seen evidence, either in my own playing or in any kind of testing I've read about, that a solid silver tube makes any difference compared to a silver plated tube, but most manufacturers reserve the solid silver for the better grades of instrument that have more quality control and plated for the lower grades of instrument. This is not always so; when I bought my Miyazawa, they claimed that their plated instruments had the same type and degree of hand work as the solid silver ones just above; so I bought the plated body.
5) Further to the above, many manufacturers offer a choice of head joints, but usually only in the solid silver heads, which will drive you to the solid silver heads if you want a choice.
6) I personally believe plated keywork is a better choice than solid silver, as the nickel silver base metal is stronger, harder, and more wear resistant than sterling silver. However, again, what the manufacturer decides they will use will drive you one way or the other.
7) I am not a big fan of the split E but some people swear by it. It does prohibit one particular trill, which I can't remember, because I don't have a split E. The "donut" insert is a reasonable alternative.
As to brands, I would strongly recommend demo-ing the following, comparing flutes of similar price:
Yamaha
Miyazawa
Muramatsu
Sankyo
Powell sonare or whatever the current "low-end" Powell is called
Some of the flute makers change model names/numbers as often as you change your socks, so I have no idea about these specifics.
Depending on your budget, some of these brands might drop off the list.
Yamaha makes very good flutes even in the student range. Personally, though, at the "high student/low professional" range, I preferred Muramatsu, Miyazawa, and Sankyo over the Yamaha (all of them at the same price). But not by all that much.
I don't know anything about Pearl but I note that the specialist flute stores don't seem to carry them that often. I would not consider anything from Gemeinhardt, Armstrong, Artley, Selmer at this point in history. Some people really like the Haynes Commercial which is available used at quite reasonable prices; others don't. But visually it does not look like a high grade flute, and it's closed hole, so if you show up with one of these while everyone else in the school band has an open hole B foot Yamaha with pointy keys, there may be an issue.
