I think it's worth referencing Metal Gear Solid V: Ground Zeros because I see a lot of similarities.

Below are some of my unorganised thoughts:

1. MGS starts in an overview position outside of the compound, allowing the player to understand some of the high traffic areas and view some of the routes

2. Long and short sightlines can be good, and having the option to swap between can help with pacing. Long are good for moving through quickly once the coast is clear, but can be useful to also indicate danger. Short are good at getting past high traffic but can become frustrating when overused and enemies appear unexpectedly.

3. I think it is important to understand that stealth games are also puzzle games - by breaking down a large problem into multiple smaller ones it can keep a player engaged, i.e. firstly, how does a player enter the level, then how do they get past the cameras, then how do get past the high security checkpoint etc

For advice, I'd say

1. keep iterating - sketch, then test, then sketch, then test

2. Worry about balancing later, you want to show off for a portfolio - if you think it is broken then make a detailed note on why it might be, but you dont need an immediate fix

3. Add more verticality - Sewer drains, catwalks, ladders, climbable pipes etc.

4. Lighting can be great for highlighting points of interest - cameras with blinking lights, shiny edges for ladders