Heatsink Question

[DDCE88]

Ok so I have designed a circuit and drawn up its PCB and I have a slight question about the heatsink I'm going to use.
Now you'll see in the images below the place where I generally want to place my heatsink. (The yellowish green area.)
My questions are:
A) Is it okay to utilize a monolithic heatsink to service multiple parts (provided you use proper electrical isolation.)
B) You will see in the second photo a highlighted area a trace falling under where the heatsink will be placed. Will this be a problem (Again assume I will be using some sort of electrical isolation.)

I already have done calculations based off of thermal resistance to to test my idea I'm just not 100% if it will work. The last image is an example of my basic modeling. I am basing it off of Dave Jones' thermal resistance tutorial videos. I know he only ever did it for one part to a heatsink, but since he said the system could be modeled like an electrical circuit (Replacing current for Power and Voltage for temps) I figured this would work. The node where every thing meets is the Sil-pad or thermal compound touching all of the components before it hits the heatsink.

[m k]

With few cases I've seen it's clearly not a concern what is finally underneath.
Though I'm not sure, maybe they were just mechanical insulations.