F-35 JSF

I’m aware that the JSF has been discussed on here many times, but I had some possibly new questions about it. Why is it that top speed will supposedly be limited to Mach 1.5? I mean the engine will produce 40,000 pounds of thrust. Will it not have a very TWR. The airframe looks clean for the most part so what gives? Is it the air intake design? Also, how many underwing hardpoints will be able to be fitted? Is it four like the F-22? How many rounds will the Mauser 27-mm cannon carry? Will it be able to carry external fuel tanks for ferry flights or increased range on missions which don’t require stealth? I guess I am just trying to get a good picture of what the F-35 is going to be like when it enters operational service. Avionics, weapons, etc. I’m mostly looking for info on the F-35A for now, but any info will do.