My baby was born at 34 weeks and, although he was a really good weight (2.46kg), his sucking reflex was under developed and he wasn't able to maintain a good body temperature so we ended up in NICU for 2 weeks. He also had prolonged jaundice (which eventually completely resolved after about 3.5 months).
NICU is an absolute rollercoaster - one day your baby will make amazing progress and you'll feel on top of the world, and the next day things won't go as smoothly and you'll feel god-awful. The best advice I can give you is to look after yourself as much as possible, eat as well as you can and rest whenever you get the opportunity.
I was adamant that I wanted to breastfeed and I was very lucky that the hospital let me stay in one of their "parent accomodation" rooms for the whole 2 weeks whilst we got established; however, I really struggled with milk supply and I think lack of rest and not eating enough was largely to blame. Being in NICU is very different to being at home so it's easy to not make time to eat and to feel guilty leaving your baby while you go and sleep, but you absolutely need to look after yourself otherwise you'll be no use to anyone.
The other thing I'd recommend is to ask the nurses to help you get as much skin to skin time as possible. I didn't realise how important this is for breastfeeding and didn't ask about this, and we didn't actually get any skin to skin time at all until day 10. Even if you don't end up breastfeeding, skin to skin just feels amazing and is such a lovely chance to bond with your baby, so I'd definitely ask for some help to do this as soon as it's safe for your baby to be out of their incubator. Some hospitals encourage "kangaroo care" for premature babies, to help you get the skin to skin time.
We ended up using nipple shields for breastfeeding, as my little boy was struggling to latch, and they were an absolute god send. We stopped using them after about 4 months (he just decided one day that he didn't need them anymore), but there's no way I would have been able to breastfeed without them. If your little one is struggling to latch because they're so small, this could be something to ask about.
Also try to remember that breastfeeding isn't the be all and end all. I felt quite a lot of pressure to breastfeed/express when we were in NICU and really gave myself a hard time about it, and I wish I hadn't stressed so much. We ended up introducing some formula after 4 months at the instruction of the paediatrician as my little boy wasn't gaining weight quickly enough. At first I felt really ashamed of needing formula (stupidly!) but it turned out to be the best thing we ever did. He's now 7 months old and you wouldn't know he was premature to look at him - he's caught right up! We're still mixed feeding and it suits us really well.
I hope everything goes well for you today xxx 💚💚💚