Lagging PC and RAM issues

You trim your shots or edit them in Premiere Pro. The shots that need visual effects are then moved to After Effects. If the effects are complex and the render times are long, you render the effects shots and replace the original shots in your edit in the Premiere sequence. 

This is how Sony Pictures, Universal Studios, George Lucas, Industrial Light and Magic, Pixar, Disney, and every other production house in the world makes movies with visual effects in them. The software may be different, but the workflow is the same. Trying to do everything at once in a single app is inefficient and the potential for disaster is huge. 

I work mostly in narrative storytelling, and I do a lot of visual effects. More than 90% of my AE comps are less than 7 seconds and one shot. Even when I do explainer videos or cut music videos that are full of effects, the longest comp is one phrase, or a couple of bars of music, or one thought and they are edited in my NLE of choice for the project. I use Premiere Pro and After Effects for about 80% of the work. Davinci for about the next 18%, and Final Cut Pro and Motion for about 2%. On rare occasions, I'll throw Nuke into the mix, but only when a client requires it. 

Probably the longest piece I have ever cut entirely in After Effects in the last 30 years was a 60-second TV commercial that was entirely motion graphics.