There is an "inbox" widget that will show pending (e.g. not yet checked) messages and (I think) missed calls, but I find it kind of annoying. At any rate, someone could write such a widget, so you could always ask around and see if a developer is interested. As for your original questions...
Regarding widgets: for the home screens, there are widgets, app shortcuts, contact shortcuts (with presence and picture), and web shortcuts (with thumbnail). New widgets can be coded as desired, and installed from the app manager, but I don't know if the other types of items can be extended.
Regarding SMS: it's been said (and complained about) extensively elsewhere, but do note that one-handed texting (e.g. with the on-screen dial-pad) is not available. You'll have to use the normal keyboard (or the landscape-mode on-screen keyboard, I suppose).
Also of note:
- this probably doesn't matter terribly to you, but to be clear, there is actually only 265MB of RAM - the rest of the "1GB" figure is virtual memory on Flash. It still performs superbly, though.
- I don't claim to have much technical knowledge about overclocking the device, but as with all such things, there are caveats, so make sure you know what you're doing before you decide to dive into that.