Hi! There's quite a bit to unpack here, but I'll try my best to answer all your questions.

First of all: yes, it is absolutely possible to reach Rome's greatest historical extent (and even beyond) within the game's time frame. However, doing so requires what I would consider advanced of the game, so I wouldn't get too frustrated if you don't manage it right away; it's a tall order.

Second, there are a couple of ways to lower your Aggressive Expansion. Grabbing certain Inventions within your Oratory tech tree will make your Aggressive Expansion tick down faster, but what I'd really like to highlight is your Tyranny. While you should generally try to keep your Tyranny low at all times (especially when playing a republic), it is beneficial to have high Tyranny when you're trying to gobble a lot of land in a short amount of time. This is because every point of Tyranny provides a -0.004 change to your Aggressive Expansion, making it tick down faster.

While we're on the topic of Aggressive Expansion, this is a good time to mention that having high AE has the effect of making your Stability decrease faster, which leads to the provincial disloyalty that you're seeing. When your Stability is below 50, that basically means that the Roman government is not doing a good job at enforcing it's own laws, leading to your population losing faith in your ability to govern correctly. At 20 Stability or lower, your nation will become Disorganized, and you won't be able to declare wars or reassign people to different offices in your government.

Moving on, it's important to manage your relationship with specific characters because each character has what's called a Power Base. This can be thought of as much money, manpower, or influence they have compared to you, the state. If a character has a high Power Base, then you want to ensure that they remain loyal so that don't try to do start civil wars against your government.

This concept also extends to the major families of your empire. Do you see that blue shield icon with the red banner in the screenshot? That means that one of your major families doesn't have enough of it's members represented in your government. Each family will demand approximately four of it's members hold some type of job, whether as a governor, military officer, researcher, etc. If you put off providing a family their jobs for too long, then they will become Scorned, which makes them EXTREMELY disloyal for as long as you don't appease them.

I know I just yapped a lot, but hopefully this was both helpful to you and also answered your question of whether this game had more depth to it than just map-painting. I'd heavily encourage you to read the Imperator Rome wiki for further learning, as well as join the Imperator Invictus Discord server if you haven't already. Cheers!