This is a PPC boat build (obviously). The whole point of the 5S variant is to have 2 AMS, so this build has 2 AMS. Because the objective with a PPC boat is to get as much fire downrange as possible, to economize on heat none of the PPCs are extended range. Therefore, in order to avoid being defenseless at close range, 2 MLas are added. With Endo-Steel and a 300 engine (standard, not XL), and losing a bit of leg armor (57 per leg vs a max of 72), 18 double heat sinks can be fitted. Other variations are possible (like switching one PPC to extended range, losing both MLas, and adding 1 DHS + 1 ton AMS ammo), but I find simplicity of weapons groupings and minimizing heat are key to functioning effectively under fire.
I use a similar build modified as above. With 2 x AMS I find I really need 2 Tons of ammo and even then in todays pug matches I am running dry. I prefer to have at least 2 ER PPC's for Pug matchs which i find the 5S better for. In 8 man drop decks I would use 4 x PPC however I think the 3F is a better chassis for that. Dropping the medium lasers allows for that extra ton of AMS ammo and another DHS to keep the ER PPC's under control. Elite skills make a huge difference in the performance of this mech and any of the stalker PPC boats due to the improved heat efficiency.
For those just joining the thread, a recent update to heat calculations nerfed the concept of a PPC boat. I would not recommend this build any longer.
It certainly has been nerfed, however I am still seeing plenty of 4 PPC Stalkers in 8 man drop decks. PPC's are now just macro'd 2 + 2 with greater than 0.5 second interval to avoid the heat penalty. You can still hit anything other than a fast moving light with all 4 PPCs and that will still hurt. But I would agree there are better choices on the field now with 2/3 PPC Gauss and the reduction in JJ reticle shake.