citizenship biometrics enroll & ceremonies

Hi All:
Many thanks for your help in advance.
I will be eligible for citizenship after 5 year T2 + 1 Year ILR soon, due to some family reasons i need to leave UK for uncertain time. i am worried about the my ILR revoke, so considering apply citizenship. I have the following questions need your help, apologies is some questions has been answered by other thread.
1) the citizenship application can only be made after 1 year of ILR? I remember the ILR can be submitted before 28 days of 5 year T2, there is no 28 days rule for citizenship?
2) all the application is online, so i can keep my BRP and passport?
3) Can the biometrics metric be collected oversea? I am planning to go to aboard within 4 weeks after submission, so worried i can't have time to find available time for biometrics collection within 4 weeks.
4) The ceremony invitation is send by POST or email? I am not sure where i will be at time, so may miss the post.
5) The ceremony has to be held in the council where i was leaving when i made application? Or i can book ceremony in any UK council ? Does it need to check my living address to book it?

Many thanks for your help
Eddy

1. There is NO 28 days early concession for citizenship, it is not an immigration application.

2. Yes.

3. No, you have to enroll biomterics at ukcvas in the UK.

4. Some get an email,many get a postal letter.

5. It will be at the council you live in unless you state another council in the inline form when you apply.