For MODs also I would recommend to look into the MOD section of this Forum
the Mod of MODs is the KB_Master MOD (as already clear from the title
)
MOD's are mostly compatible with any version, but to be sure - read carefeully the most read threads about mods (there is also the sticky thread containing the list of most downloaded mods... each mod has it's own readme)
Difficulty for normal (not too easy, not too hard) is... is.... iiiiis... NORMAL IMHO
you get all equally (100% income 100% enemy army strenght...no bonuses, no penalties... still huge portion of fun... not as mosochistic as Impossible)
Do not worry about threads where many write how easy this game is even on impossible - as Cheats are free to use from the release date and they are never ever documented (that you used them... other games will sign you in score list as CHEATER... KB not) -> so many players use cheats in one or other way, than they post their great scores here... it is single player, so don't mess with such "competition"... for the first time when you don't know all the spells/units/quests.. is normal diff. quite a challenge IMO