Update: updated for v1.6.1+ Stellaris patch on 5/16/2017
Update 4/24/2017: Have added changes that slightly decrease consumer good usage and decreased tradition costs for advancement.
Very simple personal mod that I decided to share with the world. I personally almost only play max sized maps with a small number of AI opponents, generally with a "conquer and purge everyone who isn't us" attitude. Therefore, I made some changes that honestly just make it easier to rapidly landgrab and rival even the fallen empires early on.
To install, simply unzip, take the LMH mod file and mod folder and put them into your Documents\Paradox Interactive\Stellaris\mod folder. Don't forget to activate it from the launcher.
The changes are:
1. Tech research costs pretty much stay the same regardless of expansion (both population growth and colonization), so you aren't penalized for expanding rapidly early on.
2. You can directly control pretty much every system on the map, so that sectors are no longer needed. You of course can still use sectors, but if you want to micromanage, you can.
3. Halved all army maintenance costs, so you can have twice as many troops.
4. Decreased outpost influence maintenance. Result is AI builds multiple outposts and grabs land as fast as you can in some cases. Believe it may inadvertently starve some AIs of energy though, so still tweaking.
5. Essentially got rid of influence costs to colonize planets, the post-launch annoying feature they added.
If you don't want all these changes, it's very simple to change them back. I suggest getting an advanced text-mod software like Notepad++, and changing those lines to whatever you want or to the default that's in your Stellaris\common\defines\00_defines.lua file. Right click on the file after installing Notepad++ and click "edit with notepad++" to open it up. Use the row ID numbers included in the file to make your reversing/altering changes.
Let me know if the two new changes (#3 & #4) mess things up too much, as I won't have much time to test them into the late game stages.