1. I buy underwear like some women buy shoes. Seems like every couple of months I am buying some more. I have over 100 pairs. The reason for so many is that I change underwear 2 or 3 times a day. I have a thing about wearing underwear more than a few hours at a time. A new pair in the morning and right after I get home from work. Sometimes right before bed too. Hipsters/bikinis for day wear and briefs for at home/sleep. The old ones get used for that time of the month. When they end up with holes or rips, then they get tossed. I know that I have some that I bought in college in 2002. Some of them still have the matching bras, too.
2. I buy new ones about once a year. Although I will be good for a while since I bought 8 new ones this summer and they are still in great shape. I still keep most of my old bras. Some of them because I have just outgrown the band and I think I might get to use them again. As they wear out, I use them to wear when I am doing yard work or anything that's going to be physical. I have tossed a few of them, but not that many.
3. I hardly ever buy socks because I hardly ever wear them. They usually end up with holes in the heel or toes and then they get tossed. The last time I bought white socks was over a year ago. I've worn socks twice this year. I wear sandals/flip flops even in the winter.
4. No advice on the couch. I got one when someone in my old apartment complex threw it out and the other I bought at a pawn shop. The one I bought I also got in college. Maybe I should start purging! :)