1. Yes just use your credit card as normal

2. You could get stung for at leat 4% import duty, plus a fee if they have to open and reseal the parcel, plus VAT on the price of everything

3.From 20 to 50 dollars depending on whether you use surface or airmail.

4. Your purchase would not likely be covered under UK warranties. It might well get stuffed up by the post. Plus there is something to be said for supporting your local supplier. Having said all that I have done it several times and never had a problem yet.