Which tax havens would you recommend for this and why? When should we register - early on or once we are earning a certain amount?
and welcome to this community. :-)
Your question sadly cannot be answered in its current form.
If you set up a corporation in a tax heaven, then you may indeed save on corporate taxes. On the downside:
Have a look at some of the past answers on this site:
After reading a bit, if you are still considering this, go see a really good and honest tax adviser (say, a chartered accountant who specialises in international tax law) and who knows the tax law of your home country by heart. You really, really need the services of a skilled specialist if you're considering this, the tax laws in most countries are famously complex.
If your business is in the us, you have to main tax issues to be aware of.