I'm working on E4 level scope to get Promoted, and I need help with creating Eng Plan for Projects

For creating the engineering plan, I recommend this: System Design Masterclass: Shipping Real Features To Production

If this is too heavy (likely given that you are E3), they are probably looking for the more local version which is having very detailed tasks. Here's an example from the code quality course: https://www.jointaro.com/course/level-up-your-code-quality-as-a-software-engineer/lay-out-the-plan/

Also, our team roadmapping is upcoming, how can I contribute to the team roadmap as an E4?

My expectation for an E4 in those meetings is to have some sort of opinion. I don't expect them to drive any part of those meetings, but if they are a leading voice on certain projects, that's obviously nice. 2 things to have an opinion on:

1. Project ideas to add to the roadmap
2. Arguments for or against a project already on the roadmap (presented diplomatically of course)