hi,
About the timing of the appointment, if I have my in-person appointment prior to my landing date of 3 July, would the "you must have completed 2 years' leave" requirement have been met? The Guidelines say you may apply once 'nearing completion' of the 2-yr qualifying rule. Would 30 June, 3 days shy of my 2 full years, be OK?
Yes, you can apply up to 28 days before your 2 full years are up.
Re: the passport-style photos, must they be within a certain timeframe of application? Husband had passport pics taken last year for his passport renewal. Can we use one?
Not sure - for my US visas, they had to have been taken within 6 months, but I don't know if this is also the case for UK visas.
Are birth certificates required?
No.
Are copies of the app or supporting documents required?
Don't think so, but you might want to take them anyway.
Hopefully someone else who has applied in person recently can clarify.
Finances: I can easily include UK bank statements. There will be at least one entry of a large sum being transferred into the account, where I transferred money from my US savings. If I mention "periodic draws from US savings" in Section 8, or if the clerk examines my UK bank statements and wonders where the money came from, would that automatically mean I should have included my US bank statements? I only have 1 month's originals from the last 6 months, so would love to avoid needing to order certified sets/delaying the appt.
No idea, to be honest.
You could just not include any of your UK or your US bank statements and then it won't be an issue at all.
Otherwise, include the UK bank statements and have the copies of the US bank statements available.
Remember, as you are applying in person, you can just bring everything with you anyway and can therefore easily pull it out if they do ask for it after all.
I say Husband's income meets all requirements, but now I'm paranoid - his monthly salary is 2122 starting in May when he had a raise; 100 less than that previously. Is that a believable amount to support 2 adults and 2 children (half the time) in the Southeast? 
Well, there's no official minimum income requirement for ILR under the old rules and I have never seen one refused because of finances... even when neither of the couple was employed and they were living off the UK spouse's benefits.
As a rule of thumb though, you should be able to show that you have at least the amount left over (after rent and council tax) that a UK family on income support would receive each week from the government.
This amount is £113.70 for a couple, plus £66.33 per child that lives with you, per week.
So, including the children, you need to show that after paying rent and council tax, you have at least £1067.56 left over each month... before all other expenses.
Not including the children (where is their full-time home?) then you only need £492.70 per month left over after rent and council tax.
British Diplomatic posting of where biometrics were taken - ?? I had fingerprints/iris scan done at the USCIS in my area as part of my spouse visa application. Is that office a 'British embassy posting'?
For these questions, you give:
Question 8: the date your biometrics were taken
Question 9: the address of the local USCIS center where you had the biometrics taken
Question 10: the address of the UKBA consulate that processed the visa (presumably NYC).
Biometric permit - I haven't got one, bc one wasn't issued to me under the old rules. Does this sound right?
No, you won't have one, although that's nothing to do with the old or new rules. Biometrics permits are only issued for visas that are applied for inside the UK.
Your first visa was issued in the US, so it is a sticker in your passport and you do not have a BRP.
Your ILR will be issued in the UK, therefore there will be no sticker in your passport and your visa will be issued as a BRP card.
