Welcome to MobileRead, ProHobo!
Actually, from what you've said, your needs aren't all that unusual.
I'll take a swing at your questions, but hopefully one of the others who knows a bit more details on some of them will chime in and add to or correct me.
1. As you observe, most of them seem to have a problem with Letter Sized PDFs (which is to say most PDFs), particularly if we're talking (as you seem to be) about the e-ink devices. The consensus seems to be that the iLiad is better at handling them because it's larger screen means that it has to accommodate less shrinking to make the page fit, and in lanscape, half-page mode, it'd reasonably close to full size, a lot closer than the 6" screens are going to be.
2. Take a look at the app
PDFLRF, it's only for Sony Reader. For the iLiad, there's a hack that makes it easier to view PDFs, but I'll let someone who actually knows something of it answer further.
3. There's a new gen of display coming out soon, sometime. It's supposed to be a bit faster and a bit brighter, but for now, it's only going to be on the 6" Cybook device. Whether you should wait is something you'll have to decide, but I'll point out that you can wait forever and probably never get the "perfect" device, you have to decide if one is "perfect enough."
4. For viewing Letter Sized PDF documents, yes, I'd say it's a significant difference. Looked at as a surface area question, the 8" is almost twice the surface area of the 6". If you just want to read text in a reflowable (non-fixed layout) file, then I'd say that alone isn't worth the price difference (in my opinion) but there you go.
5. I have a Sony Reader, and I've found it pretty robust. The displays are the tetchy part, in a briefcase the stock cover is probably sufficient, so long as you can put it somewhere that it won't have heavy things knocking into it all the time. There are a number of extremely creative ways to approach that (see
https://www.mobileread.com/forums/showthread.php?t=8654 and
here for a few), as well as a fellow around here that's gearing up to build really nice wooden carry boxes again. I routinely use a
hollowed out book for my travelling purposes, and it works extremely well for my needs.
6. If we're talking about e-ink, then heck yeah!
The more light you get on that display the better it looks. In the sun it's absolutely gorgeous. Add a ziplok bag and you can read at the beach without fear of sand or minor splashes.
7. Presently, the iLiad is the only one that offers a true stylus function. There is one other that's expected out from Jinke/HanLin, but ... they haven't exactly been all that good at meeting schedules (one of their earlier models is ~16 past it's announced release date, and counting).
Don't worry about asking newbie questions, none of us knew anything before we learned it in the first place, and most of that was by asking questions. So you just ask away.
