Yes, these points are exactly the ones you have to pay attention to when running -nw. For instance, I run

    gnome-terminal -x /bin/bash -c /usr/bin/screen

instead of

    gnome-terminal -x /usr/bin/screen

directly, or else I get less than 256 colors (although more than 8).

Copy/Paste works fine for me in so far as that is one of the few things I use the mouse for. (I guess, in a lot of case you use the mouse anyway to select the text you'd like to copy.)

Remapping some keys is indeed necessary. In particular, GNU screen's standard escape key sequence is C-a, which in Emacs a lot of people probably prefer to be bound to (move-beginning-of-line). But also within Emacs some keys may need to be bound using input-decode-map.

As for your launcher, one thing I did differently is that my start script does not automatically re-attach to a detached screen session, but will show me a dialog window where I can select the one thing or the other. The reason for this is that I often keep a few Emacsen running in parallel for a long time, each of which is dedicated to a different aspect of my work. If I detach one session it is not always the case that I want to continue there the next time I open a new Emacs. Also, if more than one Emacs is detached I'd like to be able to say which one I want to re-attach to.

I looked at wanderlust a few years ago when I was looking for an IMAP-compatible email client for Emacs but in the end I wasn't convinced by it. Can't remember, though, what I didn't like about it, perhaps I should give it another chance.