Bfing a full-term newborn is recommended at least 8-12x daily, and it seems reasonable that a preemie needs even more frequent feedings. You can't bf too much but you can bf too little. For LO's sake and that of your supply, why not offer more often? And pump more often too. Frequent feedings ensure higher-fat milk. That's calorie-burning on the couch for us LO's tummy is about the size of his fist, so you can imagine it fills up quickly and empties quickly on easily-digested bm. At a certain point I really wanted LO to just nap and give me some free time so I tried to really encourage her to eat eat eat but then my 'free time' was spent wiping up spit-up from an overfull baby, so in the end I just gained respect for her knowledge of when enogh was enough.
A lot of newborns root often but only feed for a few minutes, then drift off. Bfing isn't just food, it's a way to connect to mama, feel safe, get comfort, and even regulate breathing from its rhythm (and from feeling mama's breathing).
Don't fret about breast size. Babies have successfully nursed from mothers and breasts of all sizes for millenia. No worries!
Bfing has been shown to help weight loss within the first month I lost the majority of my pg weight after 3 mos of bfing, when LO began ramping up her caloric needs and I figured out how to cook my favourite Asian foods with a baby around. (I also started taking a late afternoon walk with DD in a sling as part of her pre-bedtime routine, it's good for both of us.) I'm now on the fifth consecutive week of loss. Slow, steady loss is even more important when bfing as fat tissue stores pesticide residue, which will get passed on en masse if burning lots of fat very quickly.