Personally I have not used EverHour myself but yes I have also read a lot of times that people recommend it since it is easy and fast to set up.
I have also just stumbled over this comment and think this might be what you are looking for: Help w/ time tracking / monitoring workload - #4 by Mike_Kulakov
Now regarding this have a look at the video in this article which explains how workload feature works. Basically you can select one custom field such as the estimate hours and then can set “actual hours” team members can work in a week which will then show you if they are overloaded or not. Just keep in mind this is per Portfolio, so you would have to list all relevant projects in that portfolio to ensure all tasks assigned to a person are considered.