He is cute. He dresses a little young considering you've mentioned he has an office job, but time off is time off. Picture 5 looks like loungewear and not "outside clothes" especially with the underwear showing, which IMO is not appropriate on anyone--- I wouldn't have a problem with it otherwise. His flip flops are nice quality and his feet seem well groomed. I live in the west, and we have a lot of men that wear Keen sports sandals, Chaco sandals, or supportive flip flops a lot of the year. It isn't my favorite look, but I don't blame guys for wanting to wear them, especially people that have to wear boots at work. I think what throws me off the most is the hat worn half off his head, but inside in the house. My SO wears a hat everywhere, including work but still follows military guidelines about his cover and will take it off if we are at any restaurant of any formality, will take it off at any event, and will take it off at anyone's home unless it is a very close buddy. I could see asking my BF to pull his pants up or to not wear a hat indoors because those are manners issues, but probably wouldn't fuss at the rest unless he showed up at a work event of mine underdressed or was affecting his own work performance.
That said, he seems like he has said his piece. When I first met my SO I wasn't thrilled with some of the things he wore. I pointed various things out a couple times, but he wasn't comfortable with changing at that point. After we'd been together almost 2 years he decided that he cared about what I thought and cared more about his appearance and kept things in mind when he refreshed his wardrobe. He still dresses like him, but with clothes in better condition and with better fit, has a few sharper pieces, and is respectful and dresses appropriately when he attends my work events. I showed him respect by backing off, and he has done the same by considering what I find attractive on a man and respecting me by dressing appropriately for activities with my friends or at my work. I do the same, even if it means basketball shoes!