More complicated filing this year

Hello, baffled US citizen/UK resident here. I've lived in the UK for a couple of years now so am familiar with filing from abroad and the Foreign Earned Income Exclusion, but this is the first year my UK accounts have gotten complicated and I could use some help. I have some money spread across a few current and savings accounts (one being a joint account with my unmarried partner) and a Lifetime ISA.

• I know I'll meet the minimum threshold this year to be required to file FBAR. Is FBAR something the average person can figure out how to file on their own? I really don't want to hire an accountant but I also don't want to screw it up and be hounded by the IRS (I made a mistake on my 1036 years ago and it was hellish to correct).
• Is the purpose of FBAR just so the IRS knows how much you have where, or will it add an extra layer of tax liability? In other words, if I file my taxes in the regular way and then file the FBAR, will I possibly owe additional money?
• It's my understanding that interest earned on cash ISAs isn't taxed in the UK. Is it taxed in the US? If so, is that covered by the Foreign Earned Income Exclusion?
• Do I ever owe capital gains tax on a cash ISA? For example, if I were to use my Lifetime ISA towards the purchase of a house?

Sorry for so many questions, some of which I imagine have pretty obvious answers. My partner is much more clever than I am when it comes to investments but doesn't know anything about the US tax system, so I feel like I've jumped in without quite knowing what I've gotten myself in to. 

1. Most folks prepare and file their own FBARs.
2. An FBAR is filed only with the US Treasury, not the IRS. It has no effect on tax.
3. A US person is taxed on worldwide income and gains. Unearned income is not earned income.
4. Only section 988 income (foreign currency gain) tax if the gain exceeds US$200.
 

Hi guya, thank you for the quick response. #1-3 makes total sense to me. As for #4, by any chance do you know if the "government bonus" of the Lifetime ISA/Help to Buy ISA counts as interest? I'm assuming not, but just want to double check (though I think, even if so, it wouldn't put me over the threshold to have to file Schedule B).

Hi guya, thank you for the quick response. #1-3 makes total sense to me. As for #4, by any chance do you know if the "government bonus" of the Lifetime ISA/Help to Buy ISA counts as interest? I'm assuming not, but just want to double check (though I think, even if so, it wouldn't put me over the threshold to have to file Schedule B).

Not sure about your comment about putting you over the threshold to file Schedule B.  All interest is reported on Schedule B including that from foreign banks including interest from cash ISAs.

In the USA one does not receive a 1099-INT for accounts that pay less than $10 in interest but you are still supposed to list those sums on Schedule B.

From Schedule B instructions:

"Use Schedule B (Form 1040A or 1040) if any of the following applies.
You had a financial interest in, or signature authority over, a financial account in
a foreign country......."

https://www.irs.gov/pub/irs-pdf/i1040sb.pdf

From Schedule B instructions:

"Use Schedule B (Form 1040A or 1040) if any of the following applies.
You had a financial interest in, or signature authority over, a financial account in
a foreign country......."

https://www.irs.gov/pub/irs-pdf/i1040sb.pdf

Thanks, I also saw that, and no limit on the amount of the foreign account. If you have a foreign bank account you have to file Sched B