Sorry it's taken me so long to answer these questions - I've been busy with stressing over finals during the day, then playing video games at night to console myself over my stress.
Also please note that I'm not at desktop and these answers haven't been tested, but what I would assume would be correct. If you've already tried some of this and it hasn't worked, I'm sorry ahead of time; I'll try to help you further when I'm at my PC.
1) Change the font field under the nested "ItemLabel" section of HudInspectPanel.res within the "itempanel" section of code. Just remember that you'll have to do this each place there is an instance of the "itempanel". (This means killcams in FreezePanel_Basic, SpectatorTournament, etc).
2) That's more of a font issue than anything. I'm no entirely sure, but I'm going to assume it has something to do with the security placed on the font file itself, preventing it from being accessed and used unless installed on another system. I'd double check for any ClientScheme.res errors (which it looks like you've already done), though.
3) I would assume this is done by setting the zpos of of the player list to be lower than the background of the team-colored indicator at the top, then moving the background down some so it covers up the top part of the board that indicates ping, score, streak, etc, and only leaves the players themselves. Even if this isn't how whayay did it, this method should still work.
4) All borders are in ClientScheme.res labeled under the section that starts with "/// BORDERS ///". Since you're using my HUD as a base, all of the cyan borders I used I believe I defined in ClientScheme within that section.
5) By just editing the HudPlayerClass.res file, no, not to my knowledge. That border only takes into account what team you're not, not what class you're playing, meaning that there is no correlation causing that background to be present depending on your class; only your team. I suppose if you really wanted though, you could set it up so the background was toggleable via min-mode.
6) I can't remember this off of the top of my head, I'll have to check later to be sure, but as far as I know, no; it's tied in with the total number of a certain class that you have on a team I think.
7) You can remove the killstreak from the scoreboard by making the "score_width" section of the scoreboard really high. Note that this will remove both ping and score from the board though, in addition to streak. Valve made it so that "score_width" controls both the width of your current score, as well as your current streak.
As for removing it from killfeed, that's something that you might be able to do by changing the font in your killfeed to only contain letters and no numbers so that the number itself would show up blank on the killfeed. This holds a few drawbacks though, as it means that everyone who showed up on the killfeed that had a number in their name would also have that number removed, so this prevents several problems. I would say that there isn't an easy solution to that.
Hopefully this helps a bit. :3