US tax return for UK resident member of LLC

[pigro]

Hi. I am a UK citizen and I'm UK tax resident. I am part-owner of a US restaurant, via my 27.5% equity in a California LLC (the remaining equity is held by my UK born but US resident business partner). I am entirely "hands off" in the the business, my partner has all operational & financial control.

I invested $150K (over April-Oct 2009) and the restaurant started trading in Nov 09. It is currently trading at breakeven, and the only funds I've received from the business is one payment of $5K in April 2010.

The $5K payment was made as a reduction to my "capital account" (a financial instrument used by the LLC to keep track of the members initial capital investment, such that payments are made proportionaltely to the members' equity stake, as described in the LLC members agreement).The $5K was paid into my personal US bank account in California.

Questions:

1. It's been suggested by my partner that payments made to me by the business to reduce my capital account may not be taxable (i.e. that until I've recouped my $150K investment that I would not need to pay US tax on any monies received) - this sounds highly unlikely to me (given that I still have the equity which my capital bought), can anyone advise?

2. I believe that the US uses a calendar year for income tax. As I had no income in 2009, do I need to file a return at all for that year?

3. I believe there is a minimum earnings threshold below which no US tax is due (c. $9K?).
a) Is that the case (and do non-resident aliens also qualify)?
b) If so, does a 'nil' US tax return still need to be filed where anual income is below the threshold, or can I simply not file?

4. If indeed there is no US tax due on capital repayments until my capital ccount falls to zero, would HMRC view it the same way - would the $5K I "earned" in USA in (late) April 2010 need to be declared as taxable UK income in my 2010-11 tax return?

I hope the above makes sense; many thanks in advance for any feedback.