1) This is the premium to manufacture and ship the goods, Silver is both valuable and bulky. There is also the VAT to think about.
2) Guernsey is VAT free, So technically yes you do need to declare over a certain amount and pay VAT. There is no allowance if mail ordering, in this case all of it is subject to VAT.
3) It is volatile, So it may be that you need to be held for a long term to recoup losses, but then again you may be able to exit with a profit in a shorter period. If you can get the premium down then it will help. The German VAT rate will help here.
If you want purely to have a safe store of wealth then I say go with gold. If you want a little bit of fun, and you can tolerate the risks then try some silver. Unlike shares in jessops / hmv / game if it all goes tits up then you will still have some coins to use a poker chips. Or to hold till the next market rally / bubble (depending on your attitudes) in the future. obviously this last bit may depend on your age a bit. I'm 30 so if the world was fixed tomorrow and the price went down to £5 per TOz I'd be able to hold it till someone else f***ed up the worlds finances. If you are much older then you may be less inclined to risk this bull market coming to an end with the prospects of a future one.