I believe Loremaster is once per army, and can't be taken with Teclis.
I could see the reason to limit the number of HoS's in the army, but I think maybe 2 would be better. That makes LoH a little more special.
The only problem with making it mandatory is that it would make it nearly impossible to play at a lower points level. Also, 75 might be a little high. I think it will probably end up at optional for 50 pts giving up 100 extra vps (total of 15.