Raise/Lower/Front/Back: we use PgUp/PgDn/Home/End, but since you are
I strongly advise against using Page Up and Page Down for anything other than going up and down the page, it bothers me that Inkscape (and so many other GTK applications) still do it. At the very least they should be combined with a modifier, but I still wouldn't recommend it, as they are awkward to reach keys.
I don't see how they are "awkward to reach" any more than any other key. And most importantly they're VERY intuitive for the meaning of Raise/Lower/etc - their labels are obvious synonyms of the corresponding functions. I use them subcosciously now, whereas -
Forwards Ctrl+F Backwards Ctrl+B Back Ctrl+Shift+B Front Ctrl+Shift+F
this is what Xara uses, and I _STILL_ have to spend a fraction of a second thinking before I press them when in Xara, even though I've been using Xara for many years. Very unintuitive. And already taken in Inkscape, btw.
Alteratively you could use these keybindings Forwards Ctrl+] Backwards Ctrl+[
Not very intuitive either; these keys may be good for forward/backward but again you need to think before you can map them to the up/down meaning. And they're taken, too.
It of course makes sense to look at what keybindings are used by Adobe InDesign or Quark Express because those are what your userbase are most likely to be familiar with.
Do not forget about Corel Draw and Xara (the two are similar in their keybindings). They have a sizeable following too, and Inkscape is generally closer to them (partly because Sodipodi was modelled on Corel Draw and partly because I've borrowed many things from Xara which is my favorite).
Inkscape inherited these keyboard shortcuts from Sodipodi,
And Sodipodi copied Corel Draw.
For the Tools in Inkscape I think it would make sense to have single letter keybindings (right under your fingers, eassier to reach than Function keys),
In Inkscape you already have them as alternative, see the keys&mouse reference
"Arrow": F1
This is particularly horrendous, definately goes against the Gnome Guidelines and probably goes against the KDE style guide as most applications use F1 for help.
It's logical and very convenient. I use it all the time. There are many other ways to access Help. And as for Scribus, currently it does not use F1 for anything.
Function keys are awkward enough without adding modifiers. It is impossible to have keybindings for everything so it might be necessary to reconsider any keybindings you have given to features that are not likely to be changed very often.
Function keys are for tools. Using a mix of function and non-function keys for tools will be hard to remember. And again, all Inkscape tools have single-letter alternative keys if you prefer.