When I was out in the US last year, I looked at Camcorders and considered the merits (or not) of buying one.
In the end, I decided to get a PAL Camcorder, as if you want to connect directly to a TV in the UK, you need the PAL format for compatibility, or a TV that will accept either formats (uncommon!).
The charger supplied is dual voltage, so can be used straight into a 110v or 240v socket.
The mpeg4 reference, relates to converting tapes to DVD for example, and is used as far as I know throughout the world.
As regards a Tax liability, I have no idea whether you would be subject to tax or not. I guess it comes under the rules relating to the value of gifts/products you may buy in a non EEC country, whatever value that is!! I suspect however, the dreaded VAT will come into play somewhere.