I have one issue with the making of kazard-dum If anyone here has read unfinished tales then they would know that building moria (the orc name for it) took several thousand years (started c. F.A 800) and left around c. 1300 T.A
For those of you who aren't familiar with the time scale F.A. 800 means first age year 800 (thats when morgoth still ruled the west), so 4900 years later, in the third age (one age is 4400 years) kazard-dum was left to rot becuase the dwarves had found the balrog.
Second issue with the making of a balrog. A balrog literally means demon. These demons existed before the elves in the creation of arda (earth) they became morgoths servants and were finally destroyed by the valinor (gods) in the war of wrath at then end of the first age, the balrog in moria was the only survivor. Basically make then tougher then shit (Sauron, technically was a balrog)
Also Angbad means hells of iron (quenya) (it was the mines of thangorodrim that existed under the iron mountians) you are thinking of thangorodrim, the surface fortress.
The elf fortress would be amazing to be built only built in around 200 - 300 years apiece they were built by dwarves, who worked for the elves.
Or build the halls of valinor. The dwarf after life existing in the lands west of the pelori mountains in the lands of west.