Kevin,, If have have an EAD, you can use that for employment, whenever you want to.. But then, your H1 gets invalidated and you will have to re-apply for New H1, if your green card gets into trouble.
You can have both EAD and H1, you can continue towork using H1 even if you have EAD, but you can do only one job..
If you have EAD, you can do 10 different jobs, part-time , full-time, open a company with your name and recruit someone , etc, but, that will invalidate your H1.. but again, your GC will still go on..
One thing you have to make sure is, if you are using EAD, you should continue to do the job (same/similar job) related to your filing of labor certification and notify BCIS if you are changing employers.