first off, you'll need at least 1 command squad which will contain your commanding officer. (it's mandetory so sadly, you can't have an actual commissar lead your army...)
doctrines to look at;
a) grenadiers. if by 'heavy infantry' you mean 4+ saves, then you'll need this one. gives you upto 3 storm trooper squads as Troops choices, though these guys don't have as many options as regular storm troopers...
b) iron discipline (or perhaps zealous devotion?!) no guard army can do without. gives you a near-marine equivalent Ld bonus which is always nice!
c) along the same lines, you can look into die-hards. when combined with iron discipline, your men really won't break for any reason...
d) if you want your entire army to be heavy infantry then look no further than carapace armour! now pretty much everyone gets a storm trooper's armour save.
e) veterans. if you take carapace armour, then take over storm troopers. same basic pts cost, way better options such as a 'hidden' power fist & 0-3 special weapons!
f) hardened fighters. give this to carapaced hardened vets and while expensive, you have a squad that take on space marines and win!
the main advantage to hardened fighters is that it forces most opponent's to hit you on 4's instead of only 3's...
g) priests. what's a chaos hoard without the inevitable religious zealots to keep the faith and lead the men in their debased and heretical worships?!!
as for how an inquisitor would work? simple; he's a dirty, filthy radical!lol.
cheers!