A yz125 is a race bike and thus requires a lot maintenance, likely more than you prefer. Most of the maintenance will be pretty straightforward, however costs can add up. My advice would be to look at other, less maintenance intensive options such as the crf230 you mentioned. It is more much more trail oriented than a 125, with good low end torque and a smooth powerband. 125's are hard to ride slowly, they are simply not made for it. That being said, I ride a cr125 in the woods and it works just fine.
My advice is this. Save up as much money as possible, $1000 is hard to work with, especially if you decide to buy a 2 stroke. Do not buy any used bike (especially race bike) unless you are sure you can afford any surprise, sometimes very costly, repairs (I'd keep $500-$600 dollars in reserve, minimum). As you do, research trail bikes. I think they will suit your situation great. Easy to ride slower and less maintenance. If you want a 125, I don't blame you. 125's (not just yz125's) are great bikes. Quick, lightweight, and they can be made into great woods bikes with a few upgrades. With your height, a 125 would be very tall, but you could make it work. Also look into 85's if you really want a two stroke. If you go this route however, buy the nicest, best maintained bike you can. Year and brand don't matter much when you are on a tight budget, the shape of the bike is king.
All of this is just my 2 cents, I'm sure others will weigh in 🙂