This particular panel has plenty of breaker slots below for your general lighting circuits. I just never saw a breaker panel with a spiit bus, I have seen plenty of split bus fuse panels. That was probably because fuses over 60a started getting pretty expensive.
This particular one really surprised me because of how small it was. You could put in a regular 150a load center with a main breaker and still have plenty of opportunity for up to 100a feeders using branch circuit rated breakers. Those service rated breakers have to be pretty expensive. I might understand this if it was a 400a panel and you were feeding a 200a feeder along with some other loads, still serving your general lighting from here. I did that with a 200 and a 150a feeder off of it at my house. I had the 8 slot 150a service rated breaker even tho a regular one would have worked.
It is all moot now. In the 2020 code that panel is illegal. (One service disconnect per enclosure, grouped, with up to 6 boxes instead of up to 6 in one box) 230.71
