A lot of the questions you describe are a matter of personal preference, so a bit difficult to give universal recommendations. As for the technical part:

• Qt4.5 or Qt4.6

Qt4.5 in is Extras, and also available for the N800/N810. Qt4.6 is still in flux with (near-)nightly builds available, the stable is expected with PR1.2

• Python 2.5 or 2.6

2.5, there is no other choice on Maemo 4/5

• PyQt4.6 PyQt4.7 or just PySide

PyQt4.6 is irrelevant PyQt4.7 is available to both Qt4.5 and Qt4.6 so covers a bit more ground (N800+N810+N900) and is currently smaller/more memory efficient, although I fully expect the PySide team to show some massive improvements around PR1.2 PyQt will be in Extras in three days. PySide is Qt4.6 only (=N900 only), and will be Extras ready after PR1.2, with the same caveat as Qt4.6 - it has not yet reached a stable status, so it's still a moving target. PySide's real relevance will probably show in Maemo 6, in Maemo 5 it's mostly irrelevant, I'd go for PyQt as you don't loose anything, but then again, I'm biased and am certain PySide guys will recommend PySide

An unbiased (well, at least we tried ) overview can be seen at:
http://wiki.maemo.org/PyMaemo/GUI_to...election_guide

• Pluthon, Eric4, QTCreator/Designer or PyGTKEditor

Tough one. Personally, I use QtDesigner for .ui elements and WingIDE as my main IDE as it's pretty configurable (allows on-device debugging) and works nicely with PyQt (knows about PyQt autocompletion, help, etc). Wing is sadly not generally free, though it IS available for free to bona fide OSS developers (but not commercial devs). Pluthon is also very good in Maemo device integration, but lacks the Qt touch - it does work but the templates/help/etc are GTK oriented. And, of course, Eclipse itself is a love/hate thing Eric4 is okay, but AFAIK no on-device action support which makes it a bit limited. Never tried PyGTKEditor.

I generally try to develop as much as possible on the desktop, and just switch to on-device when I start using something Maemo-specific. I usually code in a way that my Maemo apps are (ugly, but working) desktop apps, too.

PS. Oh, and a lot of (hopefully ) useful Python-Qt info can be read about in the slideshare presentation in my sig, given at the 2009 Maemo Summit