It depends heavily on what you want to use them for. PVP or PVE? Ganking, Alpha fleet or sustained DPS? Abyss? Exploration? Missions?
Generally for PVE you will want to look at Auto cannons instead of Artillery. There might be one situation where you’d want Arty (Scarlet) for example but ACs far out dps and out track Arty. This is especially important when fighting frigates.
Also keep in mind Minmatar are the only ships that really use projectiles, much like Amarr is the only ships that use lasers. Minmatar ships tend to be shield tanked although a decent number is or can be armor tanked. The shield tanked ones are best for PvE since you can stack damage and tracking modules on them. Minmatar ships tend to also be faster than other ships, this helps a lot with getting ACs in range.
Now some Minmatar ships are more suited for Arty, the Rupture actually being one of them as they have more PG than normal to help fit them and generally have ship traits suited for arty.
Another difference between Arty and ACs is that Arty has a lot of optimal range as well as falloff meaning it’s easier for something to get in under your guns. This does also means ship traits improving optimal is a good sign as a Arty focused ship. ACs tend to have almost no optimal, though not quite as bad as blasters it’s pretty close. ACs have huge falloffs helping a lot with tracking and allowing much further reach than you might think initially and ships with falloff traits should mostly fit ACs
When looking at guns sizes within the same mounting size (small/meidum/large) you have a decent bit of flexibility. For example your 720mm Howitzers has very high alpha and range but very poor tracking. Going down one size to 650mm arty sees a sizable downgrade in alpha, almost half, but a much faster rof and better tracking with only a slight (10%) decrease in dps and a small decrease in range. If you want to go with Arty look at fitting the smaller ones to help with tracking and faster cycle time and easier fitting.
ACs have similar, but much less pronounced differences when going down a size, however the gains in tracking can sometimes make it well worth it to go down from 425mms to 220mms but generally you want to stick with the largest ACs you can fit in most situations.
For Ammo you will generally not be using T2 Arty ammo as much, if at all, just the short range faction ammo (phased plasma, EMP and Fusion). For ACs you’ll often use Hail in PvE or the appropriate short range faction ammo. Sometimes barrage will be used in battleships when facing enemies that like to orbit at 40-50km.