After finishing reading the collected visions of the horus heresy artwork, i have been left a tad confused.

Firstly, the studs. There appears to be no standard placing of the studs. Whilst i know that this could be due to the different MKs of armour, there is even differences between troops who are supposedly wearing the same type of armour.Is there a standard pattern of armour per MK and this is then customised? or is the variations dependant on the legion? or has the artwork got it wrong?

Secondly, squad organisation. The squads do seem to be ordered into tactical squads but these do not carry heavy or special weapons and instead these are carried by support squads. Is this correct? or has the artwork just got it wrong?

any help in clearing this up would be greatly appreciated.

As far as I know Mk IV had problems with the more complicated design and so the MkV was invented as a stop gap.
Therefore you are possibly more likely to see more improvised variants of the MkIV during and just before the Heresy than any of the other types.
Infantry squads seem to vary with the artwork books. I personally use only bolters in the tacticals and leave the heavies for the support squads. :)

The heresy armourhad studs on the helm, left shoulder guard and both lower legs as standard the rest of the marks are random placement. :o

your image links broken at least to me coz i cant see tha pic

Basically it depended on the armourer for the armour deisgns. Depending on his tastes/likes modified where the studs were/how many studs as well.

And about squads, it's all up to the objective. Isstvan 3 (where alot of the artwork is palced, alongwith Isstvan 5) was mostly a civillian uprising, so basic marine squads carried plain bolters. Tac Support squads and Devastator squads took the heavies (all of the eggs in one basket if you ask me) for dealing with heavy infantry and tanks. The loyallists had no idea what was about to beset them once Praal was dead, so they weren't prepared!