Number 2 is also the hardest one - I don't think you can get around showing the user interface before firefox loads using a standard N800 setup.

However, you could replace the N800 window manager with something like fluxbox/openbox, that has no items on the screen if you don't put them there. I am not experienced in doing this, but you should talk to PenguinBait (from this forum), as he has done exactly this procedure to get KDE running on the tablet. There is a thread somewhere in which he describes exactly what is necessary. You should do exactly the same, only implementing fluxbox/openbox in stead of KDE. Alternatively, maybe you can avoid loading the menu and applets on a standard N800 setup, but I think this is quite hard.

There may be a better solution than *box as a windowmanager, as the N800 is very Gnome-based (mostly because of its reliance on the virtual keyboard, which only works in Gnome). So if number 2 is essential, you need to go trawling the net for a minimal Gnome windowmanager, that you can compile for the N800 (don't fear this step, as most linux gnome programs simply compile without changes if you use the scratchbox). Maybe even the builtin windowmanager in Maemo can be adapted, but as I said, my experience is limited. The alternative is *box, but then you need to supply a virtual keyboard. Of course this might even be simple, if it is just for a web-application - I see no reason, the virtual keyboard could not just be a part of your webapplication rather than the device setup.

Of course, the really simple solution is to use an N810, which has a hardware keyboard, or bundle the N800 with a BT keyboard.