I personally don't think a 375 XL is worth it in a Mech this size, but I figured I had to do something to differentiate it from my other Trebuchets, and since it can hold a 380 XL, I might as well use it. This is as fast as most lights pre-tweak, unless they max their engines. You can keep up with the light group and deal a respectable amount of damage. The only downside is that while you have the speed and firepower of a light, and more armor, you are also significantly easier to hit. This is fun, but I honestly prefer my 325 XL and jump jets on my 7M (which has otherwise the same build). Edit: Upgraded to 380 XL because someone pointed out it's the same weight as 375 XL.
You have loads and loads of slots unfilled. Adding FF will allow you another ton to play with. Also, you don't need THAT many DHS, you can take a couple off. Use the extra tonnage for AMS, SRM upgrade, and/or more MLas.