What parts of the system design do juniors(0-2YOE) usually do poorly on?

Have an oncoming on-site, and seems like grokking is apparently too surface level.

My plan is this:
1) ask clarifying Qs about features
2) define features
3) ask about scale, and do some memory calculations (how necessary is this part? Do I need to take into account OS space?)
4) figure out data model: talk nosql vs sql, database table drawings where I write the columns
5) draw high level boxes of services
6) optimize bottlenecks

Am I missing something?
How important is it to talk about actual technologies like “I’d use rabbitmq or mongodb”

When talking about protocols, HTTP is usually the answer for client to server, but I need to talk about offs right? What are the negatives of using http? I’d imagine http is the only solution here for example