Heat and Capacitor Draw are two seperate mechanics, as much as high heat will prevent you from firing, you should view them as unrelated.
Each ship has a unique heat profile (AFAIK) determining how much heat it can disperse per second. There's no way of knowing it without testing the ship yourself unfortunately.
Weapon heat generation is also influenced by the number of PIPs you have allocated to weapons. I did some testing in my FDL a while ago and determined the coefficients for heat (assuming 0 PIPs is 100%) are 2 PIPs = 85% heat, and 4 PIPs = 55%, so PIPs allocation can make quite a sizable impact on your heat generation.
Lasers I wouldn't consider "high heat" weapons. Compared to Kinetic weapons they produce more heat yes, but compared to Plasma Accelerators and especially Railguns, they're relatively efficient.
For comparison I can run 4 x Medium Burst Lasers (Efficient Mod) on my FDL with both G5 Dirty Drives and a G2 Overcharged Power Plant and heat is never an issue, and I run 2 PIPs to weapons 99% of the time.
If you're concerned about heat, I'd recommend investing in the Efficient mod, it makes it pretty much a non-issue, and is overall arguably the best mod for sustained DPS output. IMO Dirty Drives are just too good to pass up, and since I can get away with 5 x PA running them, I'm sure you can get away with a few lasers, regardless of the ship heat profile.