I got my answers elsewhere and thought I would share:
1) File FBAR.
2) File 1040, showing ALL income earned worldwide, including your self-employment on Sch C. All UK income goes on this return.
3) File 2555 and/or 1116 to claim reductions for foreign aspects of your return. To get the maths to work right, you should consider a tax programme like Turbotax or hiring a tax accountant. The maths on a self-employed 2555 and 1116 are trickier than that of an employee.
4) in your arrival year, US workdays are taxed in the US and UK workdays are taxed in the UK. You'll need to first do an allocation of US/UK workdays for your employee period, and then do a second allocation of US/UK workdays for your self-employment period. No definition of which is which. Enjoy doing the maths, or buy a programme or hire somebody.
5) Social security taxes are separate from income taxes. Thus, you don't file Form SE, since you are covered under the US/UK Totalization Agreement. If whatever method you choose results in US Social Security taxes being computed on Form SE, it's wrong; fix it before you finalize.
6) The UK year is 6 Apr 2010 to 5 Apr 2011, and your first tax return is due 31 Jan 2012. Prepare your UK SA for 2010/11 and PAY THE BALANCE DUE by 31 Dec 2011, so you can optimize your 2011 US 1040 filing choices.
7) Also prepay your first half of UK 2011/12 tax by 31 Dec 2011.
This is one month BEFORE the REAL due date of 31 Jan 2012. Do it one month early anyway.