Perhaps the size of this event is limited because of the venue. It is at a historic farm in PA. They might not be able to handle a large crowd. This farm was chosen because of the historic significance of the place. He does sound like his voice is failing a bit. He is going to have to be careful not to blow it out before he finishes events/rallies on Monday night.
If you think about it, he was doing rallies and dealing with the Seal Team getting the hostage. Now it makes sense why he was tweeting around 3am the last 2 days. MAGA2020!