Giving my site a face lift - thinking about adding some extra functionality

Now that I've got my site back (see my latest support post. groan), I'm thinking of giving the site a bit of an update.

I'm currently running 3.5.1 in a totally vanilla way. No extras really. But even before the disaster, I was thinking of implementing one of Kali's excellent new templates ("Sensible") and then taking advantage of its versatility and maybe adding some extra mods. However, I'm not really familiar with what's out there and what people are using.

So, here are my questions (finally):

• What would you recommend in the way of mods? What do you find really useful?
• Are there any big downsides to adding mods (upgrading, maintaining etc)?
• Does anyone have a scripted way of backing up their stories directory and say, emailing/FTPing it somewhere?

Thanks - I'm looking forward to your comments.