1. The 130% figure does not mean that the outdoor unit can overrun by 30%, although it can produce a little more when 130% is connected as compared to 100%. It means that the total total capacity of the indoor units combined can be as high as 130% of the outdoor. That number on the newest models is moving up to 150% and 200%. This allows you to size the indoor units such that one part of the building may need at or near full capacity as will another part of the building - just not at the same time (diversity).
2. Efficiency is about the same between the larger sizes and the smaller ones.
3. Yes, some manufactures will use two smaller compressors and others one compressor. When there are two, one is an inverter driven compressor and the second a fixed speed compressor. The system determines when one, or the other, or both run.
4. The more sophisticated PC based controls may be able to incorporate that feature.
5. Have not researched the ERV/HRV differences. Most all can incorporate them within the system though.