British Expats - FLR(M)? and documents to provide

Hello everyone,

I am applying for an extension of stay in the UK as a partner of a British citizen who lives in the UK.

Situation of my wife :

British.
Lives in the UK.
Salaried employment in the UK.
She (will) has earned more than £18,600 per annum for the past 6 months.

My situation :

Non-EU National.
I have a BRP of the type: SPOUSE/PARTNER LEAVE TO ENTER that will expire on February 2019.
I Live and work (Salaried employment) in the UK.
I (will) have earned more than £18,600 per annum for the past 6 months.

My questions/confirmations:

What type of visa I need to apply for?
- FLR(M)?
- if Yes, what is the difference between 2 year route and 5 year route?
Is there any English language requirements?
- is it IELTS Life Skills A2 in my case ?
- What is better for future visa applications, for example IELTS Life Skils B1?
As a married couple, do we need to provide any evidence for genuine relationship?
- if Yes, what kind of evidence please? some examples will be great
For financial requirements, is it possible to provide evidence from only the applicant who satisfies the financial requirements OR only the partner (British) who also satisfies the financial requirements OR both?
When is the best time to apply? before 28 days to apply online or submit your documents
Is there any documents or links explaining the procedure to follow?

Thank you for your help