1. one problem is the 'substantial earnings'. SS defines it for each year. I missed one year by 50 cents, so that year of work wasn't counted.
2. you only get WEP'd once. So if you know you are getting a UK state pension of, say, #1000 a year and know you will get a UK private pension of #10,000 a year, you'd want to start receiving the UK state pension, get WEP'd, then start receiving the UK private pension.
3. the exchange rate of WEP is the day the administrator does your case. And it can never be changed. So if the exchange rate is $2.00 your #1000 UK state pension will be equal to $2000. If it's $1.5 your UK state pension will be valued at $1500 (remember - this will result in a lifetime decrease in your SS payments so it's in your interests to have that value as low as possible).
4. Best to deal with SS in Baltimore about all these issues.