So I've been running this build for a while and it's a bit unorthodox but I love it. I rarely do under 600 damage in a game and a handful of kills/assists. I personally run it with just the 4 MLas but you could drop a ton of ammo or the half ton of ammo and shave some armor to add another. The biggest problem with this build is the amount of ammo you need to carry, but you will put it to good use. The LB5-X's throw a great spread so you can get that 25 damage on a single part or a light mech at closer ranges and still allow you to pester the shit out of people even out to several hundred meters. The lack of an AMS is a problem at times and you are vulnerable to LRM spam so try to find an ECM or a couple people with AMS to stay near. It's simple, but don't be fooled, even assault mechs will melt before this thing. Alternate 5x cERML version. If you really want an AMS you could try something along these lines with a similar result.
I ran that setup for a while and I didn't like how quickly it got hot. Inherently I try to keep the damage on the dire to the LBX and use the las to add damage on large or stationary targets because if you're aiming for the lasers you're not accounting for bullet velocity and vice versa.
This might be a good compromise (didn't want to build from scratch, but better on A or prime since it doesn't use the CT hardpoint and they have better mobility).
This lays down some serious hurt. Very first game with this build got me a 133 score and 1045 dmg. Used first variant.
This build is still amazing for 1000+ damage matches. Been running it like this for a while now, the MG rarely does anything, but losing a little ammo for it seems a good trade. Plus added a CAP.
Personally I think 4xLBX5 would be a good balance... 5x LBX5 is deadly, but there is the ammo problem, and you need to really ration your ammo. Either way it is a deadly build. My take on it... Ad a bit of JJ to make moving less painful. You don't need many DHS, since you are mostly using your LBX5 and ML is there for backup. But if you use only 4x LBX5 you can have 2x ERLL as backup and secondary weapon... Your choice really.