H1B after 6 years of working

Hi,My wife is living in USA and going to complete 6 years of stay & working on H1B by sept, 2018. I will be applying for H4 OR H4 EAD later on for her. I would like to know when she can re-apply for H1 VISA exactly again and also whether she will be falling under cap count next time when we apply for H1B . Is it possible to apply for new term without leaving US? Could you please clarify and help us about this info.I am also thinking to apply for PERM for her soon through her Employer.