How to Deal with Empire Size?

Having a really odd playthrough that I’m going through currently. My entire plan from the beginning (xenoplhobe/mitaristic) was to be a bully, subjugate a couple bulwarks, and create a federation with other bullies. Unfortunately my starting spot was near the tip of the arm of a spiral galaxy and I was blocked in by another empire. I steamrolled that empire pretty easily, but due to the placement of a fallen empire and a marauder clan, there was only one direction to expand. The surprise here was that direction was completely void of AI empires. I now literally control 25% of the galaxy (Medium) with more room to expand and am still a good 12-15 systems away from the nearest AI empire border. Since I sacrificed some of my advancement to get that big fleet early only to have nothing to conquer, and since all that expansion gave me an inflated empire size and slowed my research to a crawl, I’m way behind all the AI empires on tech and unity.

Two questions…

It’s still only about 1/3 of the way in… what are some ways I can salvage this playthrough to handle the crises (set to all)? Don’t really want to bail since it’s my first ever playthrough that spawned Sanctuary (near me) and I got Brain Slugs.

For future reference, if you have a playthrough with a lot of open space to expand and no enemies, how do you manage that empire size modifier and pivot to go wide without falling behind on tech and unity?

Thanks!