Here is my experience / opinions:
1. Do not come to the US to raise money unless you have a revenue generating firm with at least 3+ REFERENCEABLE clients.
2. If you are doing financial service or marketing automation - East Coast (NYC specifically) is OK, for anything else you want to have an address and a conference room within 5 miles of Palo Alto. As silly and elitist this sounds there is a simple reason for it - people who tend to sit on 5 to 20 boards really like to be able to drive to the companies they invest in (so that they can be home for dinner with their families), rather than have to fly to board meetings.
3. Setting up a firm takes no time at all - BUT always work with an attorney who specializes in startups and corporate transactions - I have worked with the same San Francisco council for 15+ years and she is able to turn around in less than 24 hours most of the routine corporate registration, licensing, etc. transactions.
4. You MUST consult with a tax attorney - depending on which country you live in it makes a difference - specifically you have to decide if you are going to be a C-Corp or an LLC. A Delaware registered C-corp is the default structure for a VC funded / stock-option incentivized tech startup, but there are many different variations - one size does not fit all.
5. Business VISAs are not a problem and I work with (and employ) many people in Europe who have 10-year multiple entry business VISAs (B-1) - these make it possible to spend about 3 months per year working in the US - especially if you are doing fundraising, bizdev, sales, etc. For senior staff the L-1 VISA is the best. The process is routine and is simply a matter of filing paperwork - something we learn to do well if we do business in Europe J Timing can be a matter of weeks, but rarely more than a month or two.
Since 1998 I have helped several colleagues from Eastern Europe, Germany, Norway and the UK setup in the US (and US firms in Romania and Bulgaria :) ) - I would be happy to share my contacts with you - feel free to reach out directly to me via email - d[at]Panaton[dot]com