Congratulations on the birth of your little girl! I agree with others--sounds like you are doing GREAT. Way to go!!!!
My DD was born at 31+3 and I exclusively pumped for 6 months, and then pumped/FF for a further three months. It is grueling, exhausting, and frustrating, but worth every drop. Especially when you are separated from your baby because she is the NICU, pumping is a great way to connect and feel like you are doing something to contribute to her health and well-being.
The Symphony is a great pump--I say this sitting here, typing while hooked up to one that we've rented to deal with oversupply issues for my son. I'd invest in the Medela double-pump bustier thing if you can. It's a bra with holes that the pump flanges go through so you can pump hands-free! I'd also get a Netflix subscription if you can. When you spend that much time hooked up to a pump, it's nice to have something to watch in order to pass the time
It also incentivizes us pumpers to stay on the pump a little longer. No joke, I'd put on episodes of The Office, sit there watching them and have the pump turn itself off because it had been on too long (30+ minutes?). I totally forgot that I was on the pump, and was just having fun watching TV/movies. My supply was great and I was getting around 8 oz per pumping at my peak.
As far as washing supplies, which is the BIGGEST pain about pumping in my opinion, we were very diligent about washing/sterilizing between every pumping in the beginning but later on (1-2 months after DD came home from the NICU) I would just rinse the parts in very hot water in between pumpings, and give them a good soaping up only once a day. This saved lots of time, and it saved my hands from cracking and bleeding so much.
If you are concerned about supply, I think the most important thing is to keep up what you're doing with pumping every 3 hours. Also, keep all that frozen milk! I made the horrible mistake of leaving my milk (2 garbage bags full) with the NICU for donation because we didn't have room at home when DD was discharged. When my daughter reached 6 months, I accidentally slept overnight, got a clog in my right breast, and permanently lost about 50% of my supply in it. Since DD rejected the breast and would not nurse, my supply never recovered and we ran out of milk at every feeding. You will hear it time and time again, but a pump cannot come close to stimulating production the way that nursing can.
Which leads me to my next thought… I know that in the early days they are very cautious about slowly increasing the amount of milk, so they might not want you nursing yet, but if they will let you try recreational breastfeeding in the coming weeks, I would try it. It is great for stimulating supply, and it will set you up for breastfeeding when your little lady comes home from the NICU, if that's what you want to do.
Hope this helps. Please feel free to PM me if you want to chat. Exclusively pumping is a very special kind of h-e-double hockey sticks, and frankly doing it for even a single day makes you an incredible mommy! Again, way to go!