I love the idea of using a Primarch despite his extreme points cost. What extra units should I focus on adding first? I was actually thinking of a couple rhinos for the extra troops, and then either a Medusa or basilisk. Or should I get some terminators since Perturabo gives them deep strike? I like the cataphractiis for the invul but what about tartaros for the sweeping advance and I think they’re faster too?
Extra bodies/extra Rhinos are generally useful. The Rhino is still cheap in 30k and provides strong protection against a lot of anti-infantry fire. Medusa is generally better than a Basilisk, the AP2 makes it a threat to Terminators, the S10 lets it Instant Death Custodians, and the longer range on the Basilisk isn't used on most tables.
I'd suggest saving Perturabo for bigger games; Primarchs and especially Primarch deathstars (Primarch + bodyguard squad + transport) are almost always massive overkill. Sure, you can kill anything you touch as dead as it's possible to be, but if you blow a thousand points doing it and the other guy just runs away with most of his force and grabs other objectives it's more of a hinderance than a help.
I don't see a heavy melee unit in there; Tyrants are predominantly a shooty unit and using them as a powerfist squad is a waste of potential, and while Tacticals can chop up basic units pretty well throw them into someone else's proper melee units they will go down. Consider Terminators (Cataphractii are limited by their inability to Run and are best with a transport, Indomitus/Tartaros only have a 5++ but are a little more mobile), melee Contemptors, and possibly an Iron Circle maniple (Iron Warriors giant punchy doom robots) if you have something to build them out of?
Those rapier batteries also look like a good Iron Warriorsy type of unit. Are Contemptors used much in the IVth Legion?
Rapiers are very useful, especially in The Ironfire (Iron Warriors unique Rite). Contemptors are in use with every Legion.
And lastly are conversions frowned upon in 30k? Forgeworld isnt much in the budget any time soon but I’m always good at converting bits into useable units.
Conversions in 30k should follow the same general rules as conversions in
40k: the models should be about the same size as the thing they're representing (don't plonk down a Dreadnaught-sized model crammed onto a 40mm base and tell me it's a Terminator), equipped with something that looks about like what they're armed with (the man with giant axes and no visible guns shouldn't represent an Iron Havoc), and make at least a cursory nod to the aesthetics of the force if you aren't doing a large-scale total conversion. Obliterators as Tyrants sounds reasonable if you've given them an obvious Cyclone launcher, the big Obliterator as Perturabo I'm a little iffier on given how much bigger the official model is. Absent a picture the obvious thing to use that conversion as would be a Terminator-armoured Warsmith.
You will run across angry purist communities that try and tell you that it's official
FW models or nothing, feel free to ignore them.
