DD was born at 34 weeks though was average size.
Expect DC to spend a few weeks in hospital, and spend most of that time asleep or having tests done (and not being too pleased about those...). Will be tube fed as won't be able to suck yet. Hopefully won't need breathing support but depends. Likely to have jaundice and spend some periods under the blue lights. Other likely (but minor) issues will include being unable to keep warm (so will need heated cot, hat etc), "desats" where their oxygen levels drop, and some level of reflux. They will probably have anti reflux meds and vitamins given by the nurses.
regarding BF: I suggest, get someone now to show you how to hand express colostrum into syringes. you will ideally start doing this ASAP after birth, it's slow and frustrating but will bring on your milk production. Then after a day or two your milk should come in and you can start using the hospital pumps (and pump in the night at home). Ask about hiring a hospital grade pump to use at home, they are much more effective. Ask them to do any top ups by mouth (which happens after the tube comes out) using a cup rather than a bottle so they don't get used to the bottle.
The usual pattern once they get strong enough to suck is for you to try to BF at each feed (the ones you are there for anyway), then they will give a tube feed top up. As pp said the tube feed top up can mean they aren't very motivated to BF. One suggestion (which I never tried) is to give the tube feed during the BF attempt, rather than after, so they associate gratification with BF.
It can be very tempting to switch to bottle feeding so as to get the baby home earlier (as home is not allowed till they can feed reasonably well and show weight gain) and the nurses may even suggest this, but it will be difficult to go back from bottle to BF, so if you really want to BF you may need to be firm and accept a slightly longer hospital time.
Car seat - we bought something called a "tiny traveler" which was a special insert to pad the seat out more for a prem baby. But used a normal maxi cosi seat with it.
Clothes - most "early baby" clothes start at 4lb something I think. Mothercare and Boots had decent prem ranges iirc. Depending on size and health you may find your baby is naked for a bit anyway. Hospital will have clothes to lend you.
Kit - the only prem specific thing we bought was the car seat insert. Weaning was tricky kit wise as the advice is to do it at 6 months actual so only 4.5 months corrected. So they cannot sit up yet in a high chair, or grasp food well. I used a Babybjorn bouncer chair on most upright setting, it worked well, and I spoon fed purées.
When you get home, be prepared for the baby to be a bit more tricky than the average newborn. Digestive issues (bad wind/reflux) are common and may mean your baby is more uncomfortable and less able to sleep well than the average. DD was very sleepy until her due date but from about 40-48 weeks (probably longer, it's a blur!) she would only sleep propped up on my chest or in a moving pram. (However she did have tongue tie which may have been more of an issue in this regard than being prem!)
Developmentally everything goes by corrected age so eg if an average baby smiles at 6 weeks then a 34weeker will only smile at 12 weeks actual/6 weeks corrected, and sometimes later as they have so many other things to be working on. It will feel like a very long "newborn" stage so do take care of yourself in any way you can - try to rest as much as possible now. tricky with other children though...
Please don't worry about having caused it - that is so so unlikely. Eating the wrong things would have caused an infection rather than slow growth.
Best of luck.