About to apply for a UK fiancee visa - advice needed

Hi all - I am about to embark on the UK Fiancee Visa application process with my fiancee (she is venezuelan) but she currently lives and works in Spain. This site has been really useful so thanks very much!

My question is that I am currently living in rented accomodation where we will not be living together - I am going through the mortgage process of buying a property for us both to live (mortgage agreed, offer accepted) and was wondering what kind of documentation evidence I will need to provide in order to confirm this in the application?

Also - is there a comprehensive list of required documents/evidence that I can access to help us put together the application? and will I need to send off my original passport?

My partner has suggested that we contact a solicitors to help us with this process - is this something that is recommended?

So many questions sorry! Many thanks in advance..