Two of the declarations from family and friends have to be notarized. You can get other people to write letters as well, but they want two statutory declarations. A few people on the forum did not send in two notarized declarations, and were approved anyway. I would not risk it.
You do not need a photo to prove that the applicant has met everyone on the list. A photo would be good, but is not a requirement.
For question 27, there is some disagreement. They do not mean just the one-year cohabitation required for common-law - they mean any time you stayed together overnight. So in your situation I would say yes, then explain clearly that you stayed in a hotel together for 21 days, and attach proof.
Some people would put no here, but if you do you must also explain clearly that you did in fact stay in a hotel together for 21 days. I have read many appeal decisions, and the judges clearly expect people to mention any time they have stayed together in this question. However, as long as you clearly explain that you stayed together in a hotel and provide proof of this, saying yes or no will be OK.