I'm going to be starting BLW in a few weeks and wondering at 26weeks do you start with 3 meals a day from the beginning or just introduce 1 type of food once a day initially and try something different the next day?

We just offered baby-suitable bits of what we were having. In the early days, if there didn't happen to be anything baby-friendly on the menu he'd just skip it. Milk feeds are their main source of nutrition still at that age so once he was getting that, skipping a meal didn't really matter.