With 36 weekers, I would do everything you can to try to go straight to breastfeeding on-demand. If they are breathing well and able to latch on, you may be able to completely avoid bottles and fortifier.
With our 35 weeker who was 5 lb 8 oz, we went straight to breastfeeding. He was a patient and determined little guy (still is!) and he did great with just breastmilk.
With our 31 weeker who was about 3 lb 9 oz, we started with an IV/PICC line and when he was a few days old he began to get breastmilk (I was pumping like crazy!) through an NG tube. We had the NG tube placed through this nose (not mouth) as this helps to prevent oral aversions. We also started kangaroo care with "practice" breastfeeding as soon as he was stable. At about 33 weeks he began to latch on well, by 34 weeks he was getting almost all of his feeds by breast. At that point, we took out the NG tube and let the NICU give him 2 bottles a day fortified with HMF and then neosure.
HMF is only available at the hospital and neosure can be bought commercially. HMF is more concentrated than neosure and is typically used with smaller babies. There are some good reasons to fortify, especially for babies who are very small or not growing quickly.
When we went home with our little one, we went straight to exclusive breastfeeding. He has grown really well (9 months old now), but we're still dealing with anemia. We fought a lot with our docs about polyvisol, but his iron levels are still low at 9 months, so...sometimes there is a good reason to suppliment.