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Delaware company incorporation: good idea?

If it is a disregarded entity (single-member LLC where the member is U.S. non-resident alien), the brokerage house or the bank does NOT send any reports to the IRS themselves. Therefore, your local taxman will NOT find out about the existence of your LLC. Is that correct?
 
A single member LLC owned by a non-resident alien (non-US citizen not living in the US) is considered a foreign-owned disregarded entity.

As long as the foreign-owned disregarded entity does not have any effectively connected income aka does not have any real physical presence in the US such as offices, employees, warehouses, representatives, other US companies working solely for it, the US LLC is not subject to US federal income.

However, it still needs to file a pro-forma 1120 + 5472 to report all the transactions between the LLC and it's foreign owner. In this case the owner still does not need to file a 1040NR personal tax return, and does not need a personal tax ID in the US (called ITIN).

However, form 5472 does contain personal information, so the IRS will know who you are. Which doesn't really matter since the bank will have it anyway once you open the bank account for it.

Investing in financial instruments such as stocks and bonds is a bit different, dividends are subject to 30% withholding tax, and the owner would need to

A single member LLC owned by a non-resident alien (non-US citizen not living in the US) is considered a foreign-owned disregarded entity.

As long as the foreign-owned disregarded entity does not have any effectively connected income aka does not have any real physical presence in the US such as offices, employees, warehouses, representatives, other US companies working solely for it, the US LLC is not subject to US federal income.

However, it still needs to file a pro-forma 1120 + 5472 to report all the transactions between the LLC and it's foreign owner. In this case the owner still does not need to file a 1040NR personal tax return, and does not need a personal tax ID in the US (called ITIN).

However, form 5472 does contain personal information, so the IRS will know who you are. Which doesn't really matter since the bank will have it anyway once you open the bank account for it.

Investing in financial instruments such as stocks and bonds is a bit different, dividends are subject to 30% withholding tax, and the owner would need to file a 1040NR personal tax return in that case.

Capital gains on stocks are tax free though.
"dividends are subject to 30% withholding tax"
Dividends from US domicile stocks are subject to withholding but UK or other countries domicile stocks are tax exempt I hope? And what about options or future trading profits they are tax exempt?