All screenplays are structured fundamentally with a 'three act' concept: intro, action, resolution. Each of those pieces can be teased apart in different ways. Writing for television (or a series) requires very clean style. A very good guide is that every five pages has a minor beat. Every 10-12 pages is a major beat. So in a typical series you have:
TEASER: 2-3 pages title sequence & commercial break
ACT I: 10-12 pages commercial break
ACT II: 10-12 pages commercial break
ACT III: 10-12 pages commercial break
ACT IV: 10-12 pages commercial break
TAG: 2-3 pages credits
From practice, I find this tends to be about where my writing naturally breaks. Write your feature and see where your breaks fall. If you decide to go the series route, look to break your episodes along the 10-12 page block units. They are points of dynamic tension that can serve as hooks and/or resolutions as they often follow on major transitions.