I was hoping you experts could lend a hand please.

1.19 - Have you lived with your sponsor in a relationship akin to marriage or a civil partnership at any time?
Yes - give details. No- Give reasons why never lived together.
I'm not sure if there a better way to word this, but essentially I was travelling in Mexico and had an apartment with a friend and she lived with her family close to her work whilst we were dating.
Unsure if I need to expand on that?
1.9 - Are you seeking permission to come to the UK as a fiance to enable your marriage to take place in the UK?
This is a yes for us, it goes on to ask if 'yes' when and where do you plan to marry?
At this point we have not decided since we thought we'd need a granted visa prior to making plans and also I don't want to get my hopes up and book a wedding! Any input on this would be great.
2.8 - Do you intend to work in the UK?
My fiance does intend to, yet we both know she won't be able to until she has fixed leave to remain on the marriage visa...Not sure what to input? Plan is for her to live with me, for us to then marry apply for the next visa and then for her to seek employment when she is legally able to.
We are required to meet the £18.6k with no child dependents.
3.3 From the list below, please indicate the main method of meeting the financial requirement.
Income from salaried employment in the UK (this is for me)
I am currently employed in the UK.
3.11 What is your sponsors annual income from this employment before tax?
This is a question I'm unsure how to answer.
When I started my full time job on the 6th July 2015 my base salary was £15,500.
I have guaranteed overtime at my job and my months went as followed:
month 1: £1,821.
month 2: £2,120
month 3: £3,830
month 4:£2,963
month 5:£3,320
Internal promotion (new salary £20k didn't make month 6 cutoff which left a shortfall)
month 6:£1,626
month 7: £3,351
so I don't know if I should put my annual salary as 1626 *12 or 15.5? or what really?
Since having the internal promotion I've not had 6 pay slips at it but I'm still at the same company.
I sincerely appreciate your help in advance,
Daniel