Thanks for the effort Jaro.
Much of the response is sensible, but some strange stuff in it though:
It is a good concept but has the problem that the molten-salt can not provide sufficient heat capacity to remove the heat fast enough.
In order to manage this problem, the fuel circulation speed needs to be very fast, and the fuel needs to be diluted very strong.
Molten salt has excellent heat capacity. FLiBe has 2.7x the volumetric heat capacity of molten lead. The only advantages with lead would be that you can have lots of it without excessive fissile inventory, so a less constrained heat exchange design is possible.
To reduce flow rates, increase delta T through the core. This is much easier to do without fuel rods in the core, as you then would have to deal with both high temperature differentials and high neutron flux in fuel rods at the same time. I've read PWR work where uprates were considered by increasing the delta T across the core, but they quickly ran into primary and secondary (Sm) thermal stress limits. This is one of the biggest problems that developers of supercritical water cooled reactors face. If you have just graphite then you're out of trouble, as refractory graphite floating about in salt (almost no stress on it) isn't bothered by high thermal differentials.
One of the issues with lead coolant is it's great weight. Perhaps, with heavy solid fuel, this can be used as an advantage, if the fuel has similar specific gravity as the lead coolant. If the net weight of the fuel is low, its deadweight stresses are low and it doesn't need such rigid connections that cause high secondary thermal stresses. It would just have to be kept in place by some sort of structure, preferably a silicon carbide composite structure, perhaps with hold-down springs or such to accomodate thermal and irradiation growth.
Hot thorium metal has about the same density as molten lead.
I wouldn't use MHC as cladding. The central station AHTR work wants to use this material as control rods!!! The neutron economy will be terrible. I would go for either TZM or triplex SiC.