Generic questions on stackoverflow can be nice, since more people will benefit from a generic answer. However, your question is probably a bit to generic. At the very least, you should consider making it a community wiki. I will try to address some of your points.
There are no clear cut answers for when you need your own hardware. However, as long as you don't have much confidential data, lean towards shared hosting. You can get shared hosting from two different ISPs and have simple coldfire failover. Just setup automatic remote backups. Hosting is cheap, and CPU/ram is plentiful. Below are some guidelines for avoiding storing confidential data.
Don't store credit card information. Find a service that will do so for you, or make your users enter there credit card number every time. If you plan on having lots of repeat customers, consider using amazon, ebay, a yahoo storefront etc.
Encrypt your users passwords A list of names and addresses is of little value, without social security numbers, credit card info, etc no one can do anything with it but send you junk mail. However, encrypting your user table is cheap insurance.
As far as overseas hosting, I know hosting in the US is really cheap, and expect the same in Europe. Web hosting is hardware and natural resource (for the generation of electricity) intensive, salaries are not a large factor in hosting. I don't see a potential for significant cost savings for web hosting overseas.
Also, there are some inherit risks with hosting overseas. The first is that natural disasters can lead to cut undersea internet cables and server outages. The second is, if you are collocating your own hardware, visiting the site is cost prohibitive. If I have a US centric E-Commerce site, I can host my hardware in New York, and have fail-over sites in Texas and California. Putting two technicians on a plane to Texas or California with backup tapes from New York is feasible. So is having my site back up in 24 hours. Put my fail-over in the Phillipines, the plane trip alone will be 24 hours, and I will have to fly my technicians business class so they will be able to rest on the plane.