Fiance visa...Questions!

[SofiaRand48]

My fiance and I have been together for over a year and a half and are planning to be married in June 2015. I currently reside in the Russian Federation and hold a Russian passport, but would like to join my fiance in the UK. We are planning to apply for the visa in February or March 2015, we have read that we need to provide at least 6 months worth of paychecks in order to be eligible for the visa, and he will only begin his job on the 28th of July. We love eachother very much, and having been in a long distance relationship for around a year now, we are very desperate to end the long distance phase as soon as possible. We will still be very young at the time that we plan to apply for the visa (he will be 23 and I will be 21, and being rather inexperienced in such matters we have quite a few questions, so we are starting to prepare for the visa now.

We are aware that we need to provide the following evidence:
I will write the documents and evidence I am aware of in bold, and write questions that concern me below.
If there is anything missing that we need to provide, please let me know!
A. Financial documents
1. 6 months paychecks from work- sponsor
2. Bank statements-sponsor
3.My paychecks from work
4.My bank statements
5.Evidence of my fiance's studies
Q: My fiance earns 21 thousand pounds a year. This is more than the 18600 required for the visa, however, should we try to save up as much as possible in a bank account? Also, as he only recently graduated, he has a rather large student loan to pay out, is this a very serious problem? Also, he has several bank accounts, and his student bank account has an overdraft of -2000. He will try to pay this off as soon as possible. I am pretty sure we need to provide evidence of all bank accounts, is this correct? Will it be a very serious problem if he has not completely paid off this overdraft by the time we apply for the visa?

B. Tenancy agreement
1. Tenancy agreement
2.Independent property inspection report to confirm there will be no overcrowding
3. Photographs
Q:My fiance will be renting a flat with 3 other young men, mostly students. He will rent a large room with a double bed in a spacious flat so there will be room for everybody. He will have plenty of money to pay for rent. Is it a problem that we will not be the only ones living in the flat? Do we need to provide some sort of evidence beside the tenancy agreement? Do we need to provide evidence that the owner of the flat will be aware that I am moving into the flat?
C. Evidence that we are a real relationship
1. Birth certificates
Q:In what form should we provide this evidence? We have an overwhelming amount of photos of us together, photos of me visiting his family and he visiting my family. He was an exchange student in St. Petersburg for a year, after which we visited eachother very often. Do we need to provide any sort of written statement?If so, how should we best write it? Do we need to provide any sort of letters that we wrote to eachother, or perhaps excerpts from online conversations? Will we be required to undergo an interview? Do we need to go to the interview together? I have heard that letters from family and friends comfirming that we are a real relationship would be a good addition.
D. Evidence that I speak English
Q:I am aware that I need to take an English test. What would be the best test for me to take? I have lived in the states for 9 years so my knowledge of English is very good.
E. Proof that we are planning to get married
Q:Would a letter from a priest suffice? Should we provide further proof, such as venue bookings, who will be bridesmaids/best man, and other wedding plans?
F.Passports
1. Evidence of my fiance's British citizenship
2.My current and previous passports

If there is anything else that we should provide with the supporting documents, please let me know!! There is another thing that I am worried about, when I applied for a visiting visa last August, I had my fiance's mother write the invitation instead of my fiance,stating me as a family friend, since it was her house I was staying at and it was she who was my sponsor. I only mentioned my fiance in the section of the application where we are supposed to write down our friends. Could this be a problem in the application? I have a vast amount of photos of us together during this visit, and supporting letters from friends can support that we were a genuine relationship at the time. I would very much like to know how our case stands!!
Thank you very much to anyone who takes an interest!!