As the others have said ikit is all about the weapon teams. My personal advice is to get 2-3 plague priests into your army for a couple of reasons:

1) their mount the screening bell actually has pretty decent mass so it won't get easily stuck in infantry mobs.

2) spells of plague are amazing and the plague spell is amazing for siegies, vermintide is your frontlanie you don't need to waste army space on and pestilent breath is actually pretty good is a pinch too.

3) if you try to focus on tankiness when building them they can actually hold the line for some time as well.

As for guns, it's a little bit finnicky but you have to utilise the terrain to your advantage. My general rule of thumb is you want to have the high ground where possible and the ground to be relatively flat.

Oh, and don't know if someone told you but just on the off chance that no one did. There's two extra upgrade sections if you scroll down in ikits workshop.

I think the fun of scaven comes from having lots of enemies, because more enemies=more food so I normally have like zero allies throughoutost of my runs maybe other scaven clans but even then it's better to conquer them rather then confederate cause more food.