I only know that there is a private sale first before IEO and if ever you do both ICO/IEO, it is going to be complicated for many people to understand. IEOs were basically created to make FOMO because it's only done on a day but it can finished in minutes or seconds. While ICO last many months to give people more time to buy so less FOMO. If ICO is done first, then people who will see your IEO won't like it because the ICO probably not sold all  which happens everytime. But if you do IEO, then it will also not go rushing to buy because they know there is still going to be an ICO.