1024x600; I've never heard of any intermediate resolution like that, and I expect 900 would be at least as expensive as the full 1024. I'm cautiously optimistic on this, though, as there are 1024x600 4.8" screens out there, and it seems likely that N810 and N800 sized models could be made with a 4.8" screen.
I think I've commented on this 3 times in this thread, so I shan't bore everyone with a repeat; I do seem to be in the minority. I guess I'll just have to get one of those protective cases like they make for iPhones; the ones that ruin the sleek design by adding the bezel that shouldn't have been left off.
That won't happen; between the weaknesses of the FAT filesystem and the way apps live in the filesystem, the only practical option available is to union mount an imagefile on the SD. Which is still quite untidy, and I can't see Nokia shipping such a thing. The other possibility is a native SD boot from the internal MMC interface.
40 GB is only useful if Nokia intends to market it in the PMP direction as well -- they could, but they'd need to ship mplayer and a front end (probably Canola), and they've not shown interest in pursuing that market segment so far. 16GB or 32GB seem much more likely than 40, as well, since moviNAND part numbers are defined for 4, 8, 12 and 16 GB. (That's the 2GB internal SD used in the N810; at least 16GB are available now.)

As for the card slot "that can fit all card adapters", I'm not sure what that means, because none of my 3 laptops has any such thing. The union of my laptops' card slots would be: ExpressCard/34, SD/XD/MS, and type III PCMCIA, with no laptop having more than two of them. If you meant either an ExpressCard or PCMCIA, I can't see how those could be fit without substantially enlarging the device.
To support XD (which are much shorter than SD), the combo slot leaves the SD sticking out partway; none of these are suited to a pocketable device, IMO. One reasonable option would be a CF slot, which would allow a CF->PCMCIA dongle, except that PCMCIA is essentially dead; SD and USB seems like the most useful possibility without wasting a lot of space.
I don't know how you're measuring RAM usage, but I'd guess you're counting stale file-backed pages. Don't. (Even more memory is almost certainly coming, though.)
It's practically certain it'll be an OMAP34xx SoC, which can be expected to clock in the 0.8-1 GHz range.
Well, we're pretty much there; while some more open hardware would help, solutions using Nokia's proprietary stuff are already there, and what's left is

1. much more software than hardware dependence
2. not really about Nokia's image

So the N900 release should have practically nothing to do with it.
Silly me, I wanted fun games, and amazing, eye-catching 3D graphics hacks (from xscreensaver, mainly), but anyway, it won't have a graphics card. That would make it just a bit large and clunky. It will, provided it has an OMAP34xx, have PowerVR 3D acceleration in the SoC, putting it in line with the best smartphones and iPhones.
Don't have, so can't really comment, but I hope they have at least two models: one like the N800, and one like the N810.