Trying to adapt from Postbox but need a little clarification

Another longtime Postbox user attempting to migrate here. Going all-in and trying not to get hung up on nuisances like the auto “reading” of emails on a folder switch, or lack of more robust rules and archiving. But having the Sanebox service manage my folders and triaging for the past 5 years has been flawless so I was hoping not to run into any major roadblocks, and am trying to take advantage of features and performance that Postbox lacked.

However… I got two things going on here that are troubling me, because they’re causing me to miss important emails (and I don’t get a ton). A few days ago I realized that I was getting a lot more messages than I thought because I had folders collapsed and there was no indication a nested/subfolder had a new arrival. It appears this is by design and unchangeable?

I was trying to adapt to this, but now I’m finding I’m getting replies to some emails I wrote this week, but they are showing up as “new” Sent messages?? I never thought to keep an eye on my Sent box while awaiting a reply. Usually if I initiate an email contact it’s to someone important like a teacher and I expect to see the reply in the folder for that school domain (which is difficult if I don’t have the “Education” folder expanded…), but now everything is going to the Sent mail and not joining a conversation in the appropriate folder.

It’s hard enough to manage email communication in general these days, but to not be able to see the most important stuff coming in is making me very nervous. Is there a setting I’m missing??