As long as it's not a reserved URL character it should be fine. A file name that starts with a dot might cause issues with some web servers but not Google. Avoid using other reserved punctuation, however (i.e. ?, &, etc)

Depends what you're aiming for. The largest difference between mobile and any other browsing experience is real estate. You're extremely limited on a normal mobile browser vs any other venue. In this realm, the iPad is generally not considered mobile. You tend to get the same browsing experience you would get on a full computer.

Another difference is that no iOS devices support Flash (that includes the iPad). Adobe has also announced that they are dropping Flash support for mobile devices which leaves support for Android tablets in the future in doubt.

Remember that having a country domain does play some role in ranking well in country search but it's not such a large role that it's insurmountable. It's possible to have a .co.uk rank well on .com and vice versa. A much larger role is played by the site content and where your links are from. It sounds like (based solely on your numbers) that your .com has more links to it. If those links are recognized as being UK already then it wouldn't surprise me that your .com is winning. What does Open Site Explorer show for your backlinks?

One thing we do is we don't give you a session on your first hit. Since your cart is tied to your session, going to the cart without one just generates a "Your cart is empty" page. If you're a customer you'd need at least 2 hits to get to the cart and once you have a session it lasts 30 days. This cuts down a ton on bot problems with the cart. Yes, this is a technical thing (and probably not something your developer can do) but I've always found it useful.

Also, I once made a newbie mistake of making an item that could be added to the cart via a GET. Don't do it! Adding to the cart should always be a POST.