Despite being extremely wealthy, Derek doesn't seem to have a lot of items or possessions. Granted he may have had a ton of stuff back in New York since he only returned to Beacon Hills looking for his older sister Laura.
Although, it wasn't revealed until the fourth season that Derek had a lot of money you could still tell that he must have had at least some kind of money. Because in the first season, he may have been living in the burnt out shell of his family's house but was driving around in a 2011 Camaro. Even though the car is some what affordable ranging in the price at the time of $29,000+ - $34,000+, he had a cell phone, wore relatively fashionable clothes and was well groomed which means he at least spent money on that. But as far as was shown that's all that he must have spent any money on.
There is no way this house still had running water or electricity, it only makes you wonder where he was going to take care of his simple basic needs such as food/water, hygiene, etc.. It does make you question his state of mind if he was choosing to live in this house, mind you the home where most of his family died in a fire.
I consider Derek's minimalism in the first season due to circumstances but since he continued to stay in Beacon Hills nothing really changed. His minimalism continued into season two where he may have become an Alpha but traded in one depressing location for another. He went from the burned and dilapidated house to living in an abandoned warehouse where he still had a relatively small amount of possessions. It felt like his state of mind was projected into his living situation as if he's not worthy of living some where nice nor surrounding himself with worldly possessions. But it also made me think that perhaps it wasn't just the trauma of the situation but that he may not want for much. Things mean nothing when your family is gone.
My theory of Derek being a minimalist was cemented in the third and fourth seasons. And thankfully by the third season he moved into a large and spacious industrial loft apartment with a great balcony and he also bought a new SUV. It seemed like he was becoming a bit more stable and his mind more at ease. Even his loft had a calm and quiet feel to it, despite the numerous distractions of people randomly showing up at his place.
His apartment although rather large has sparse furnishings with a bed, a couch, a coffee table, a long desk/table, side table and few other items. There was still some furniture in the old Hale house and I was surprised that none it found it's way into his new loft but that probably was a good thing. Derek is riddled with enough guilt as it is and didn't need the constant reminders. Since they never showed what's on the second floor, I have a theory that's where he keeps all his books and maybe even a nice chair where he can sit and read. But again that's just my theory.
I can't believe there was no furniture on the balcony, it would be a great place to read. I could see placing a nice indoor/outdoor chair with maybe a side table or bench out there. It's definitely a lounge worthy space.
Viewers didn't find out until the season 4 episode 11 "A Promise to the Dead" that he owns the entire apartment building. Not a bad investment, he makes money whenever someone buys or rents one of the apartments in the building.
In a way Derek was still rebuilding his life following the fire that killed most of his family and destroyed his family's home years ago. He struggled with the guilt of the tragedy and I think from that he found that a simpler/minimalist life made it easier to live and for moving on.
Is Derek Hale a minimalist? I think so and it's not like he can't afford to buy things he simply chooses only to buy what he needs.