I don't think the Reds will bring up a lot of guys on September 1. The AAA season continues and I don't think the Reds will destroy the Bats just to have more guys sitting on the Reds' bench.
My guess is Chapman comes up on the 1st. I also think the Reds will send Francisco down for Harang on the 31st - then Francisco will be restored to the major league roster the next day as some bench insurance. Jordan Smith could come back on the first, although maybe later in September.
Later in September, as the Bats season draws to an end, I'd expect more guys to come up. Maloney and Fisher are two who should come back. Alonso is a possibility, he's on the forty man roster.
The only real question I have is about Corky Miller. He's not on the 40, but should be with the Reds in September. Would require another roster move.