We talk about this quite frequently.
Tin plating is optional.
Regarding flux. Most electronic solders have a flux core. If you do not tin plate the PCB using a flux pen will make soldering easier, esp if it oxidizes a bit. Either rosin or no clean is ok. Cleaning after soldering is not a bad idea with either. I use dish soap and a tooth brush.
For non SMD boards I spray the freshly etched PCB with a very thin coat of clear acrylic. The heat from soldering will remove it but you may take an extra second. Some people like this method, others do not but I expect they have the acrylic too thick.