Hi There,
Send as much information as you can. They will send all the documents/pics back after doing the assessments. You can send bank account statements(If joint account), 20-30 pics. More you send less chances they will ask for more that may save some time wasting. Yes you can send all skype, facebook chats, reference letters from your friends stating they know the fact that you guys are in genuine relationship. Any other receipts you may have from your lunches, dinners together Any air tickets, hotels tickets, etc can be helpful as well. Send phone bills, tenancy agreement showing your names together will be good as well.