2018 FLR (M) Application: Self Employed, Switch from Tier5 YMS. New Zealander

Hello,

Hoping anyone can help with a few queries on the below, or just generally a shared experience because this is an incredibly stressful time!

I am on a Tier 5 YMS visa from New Zealand. My fiancee is British. We are getting married in early April, and my visa expires in May 2018. I've started the application to have everything "ready to go" and it is extensive and complex, made harder so because we are both self employed.

Background
Originally, I was promised sponsorship (Tier 2) through my position with a permanent employer They are having considerable delays with the issue of their licenses to sponsor, so both parties decided it was best for me to leave that role and go back to freelancing (self employment through my Limited company) and earn more money. This has also meant my partner and I are to now go down the route of a spousal visa. We gave notice as soon as we could and our small wedding (registry office) is booked.
--> Is it worth including this in the application itself? I have a letter from HR at my permanent position explaining the situation. I thought it may help explain why our wedding was so quickly organised, and is so close to the visa expiration date? We will be applying for this visa a mere two days after getting married.

Income requirements
I earn £35k+ p/year and my partner earns £60k+ p/year. Because I have freelanced on and off though my financial year through the Limited company sits below 18k, as I switched to permanent and was earning £35k.
--> Not sure what is best here. I am clearly a working woman, but it may be safer to base the income requirement solely off my partner as the higher earner? Do people usually submit ONE proof of income, i.e. so one person, or is it better to show BOTH (two people's income)

Help
We looked into having a lawyer handle our application but at a quoted cost of £4.5k we are going to try ourselves first as this is an enormous cost.
--> Does anyone recommend a lawyer for slightly more complex applications? Safe to do yourself?

Premium Service Booking - HELP WITH BOOKING AN APPT!!!
--> We plan on using the same day Premium Service but at the moment, I can't book any appointment for April. I have read it's 45 business days in advance, but the email from Home Office has said 42 days. Currently, I can see appointments but I can't book them for Glasgow in April. Any insight into the booking process is helpful as it seems this is a quite new way for them to take bookings.
--> Also, is the date of application the day you visit the PSC, or the day you print your complete application off (dated)? We will be doing this a mere few days before the PCS appointment as our wedding is booked early April and we obviously require the certificate before moving along with anything else.

Substantiating the relationship:
We've been living together for over six months and in a relationship for over a year. My fiancee owns his own house, we have one joint bank account in both our names and two bills in both of our names. What else have people supplied? Statements from each of your living expenses? We are in a genuine, loving relationship and have a tonne of photos etc from the past 14 months, how do you "prove" to Home Office that the relationship is genuine though?

The actual appointment
--> On the actual day, what is the tone of the staff there/ Have heard such conflicting and mixed reviews. Already very nervous so any insight appreciated. Are there any questions about your relationship we should be prepared for?

Thanks for reading this - any info you can give greatly appreciated.