This doesn't hit all of your checkboxes, but I like it quite a bit so I'll throw in a recommendation for an Anne Pro mechanical keyboard. I picked one up a few weeks ago because the robber dome boards at work were hurting my fingers. It's a pretty great board, but I'll go through your concerns so you have a decent rundown. For background, I've also got a K70 at home (cherry browns) and I went with cherry reds on my Anne.
Must haves:
- QWERTY layout = affirmative
- Full-size shift keys on both sides = affirmative
- Straight layout (i.e. no per-hand section or curved setup) = affirmative
- Tactile marks on F and J keys to assist with blind typing = affirmative
- Compact but not tiny: between 250mm and 350mm would be ideal, but I'm willing to go a little larger if it helps with the other requirements = This board can fit inside the box it was shipped in for protection and prevention of accidental key presses if you leave the bluetooth on, and then that box fits extremely comfortably inside my briefcase. The box is about the same length and height as my compact umbrella, but obviously a bit wider. You could definitely buy a case of some kind that would be more fashionable. I would say this keyboard is definitely smaller than what you stated you were looking for, and I was definitely a bit hesitant to buy it because of the size. That being said I have not found it to be a limiting factor since this isn't my primary board for home use. I probably would not buy it for that kind of use, personally, but it's excellent for portable use.
- No trackpad = affirmative
- Mechanical switches. I love the Cherry MX Red switches on my K70, something similar would be great = Comes with genuine Cherry switches in a variety of styles.
- Clearly separated function keys: so some space between ESC and F1, between F4 and F5 and so forth = Not gonna lie this one isn't so great. It's a compact board, and I'm still getting used to it as I've never had one before. I can definitely say that I'm getting used to the functionality and my speed is getting a lot better as time goes on. If I were using it at home as well as work it'd be even faster.
Should haves:
- Wireless - Bluetooth 4.0 built in, also has a USB cable.
- Under $100 - Provided you can find them in stock they usually weigh in around $85.
- Basic media keys (play/pause, stop, next, previous, mute, and volume control) - Programmable keys covers this
- Regular section for Insert/Home/Delete/End/PageUp/PageDown keys - Negative
Nice to haves:
- Not too loud - Depends on the switch type. I got reds, have gotten no complaints at work from people who have never heard of mechanical keyboards before.
- Wrist-rest - negative
- N-Key rollover - affirmative
Not important:
- Numeric keypad. That is, I even prefer not to have one because it saves space, but I won't dismiss options that do have one. = negative
- LED lighting. = affirmative and it's pretty cool, lots of different modes, etc. Can be hardware disabled via keyboard shortcut.
- Programmable keys. = affirmative. Pretty useful for this board actually, it's got three different layout presets for different kinds of interfaces and has a fourth that is completely custom. I use a pretty specific database application at work so my preset will be based on streamlining how I interact with that program.
- Scroll-lock key. Who uses that anways? :D = It's there, I've never used it.
Stuff you should know:
They've got a subreddit with guides for everything to do with this keyboard if you decide to get it. Firmware update and app installation (needed for the custom preset, I haven't done it yet that's happening this week) are a bit of a pain from the looks of things, but not too bad. There is no physical power switch. The company says you can just disable bluetooth and RGB and that will put the board into a kind of sleep mode, but you'll notice on that sub that a lot of people install physical switches to kill power and avoid accidental key presses while carrying the keyboard in a bag and having it connected to a mobile device like your phone. The mod looks easy and I'll probably end up doing it myself, most people say it takes less than an hour.
It's not a perfect board but I'm liking it an awful lot. Amazon has the red switches version in stock here: https://www.amazon.com/Mechanical-Pro-Bluetooth-Backlight-Smartphone/dp/B06XW87X9D/ref=sr_1_5?ie=UTF8&qid=1498494412&sr=8-5&keywords=anne+pro+keyboard
Feel free to ask any questions if I missed anything.