I frequently take 3-5 irregular orders. Though if I’m playing USAriadna I may take more. It kind of depends what I’m trying to accomplish with the list and how many regular orders I can get in. In general, I try to have 2/3 of my orders as regular orders on the table first turn. Irmandhinos and antipodes are good, relatively cheap irregular orders that are extremely flexible. Hardcases and Desperadoes can also be roadblocks or throwaway pretty quick. More than a specific number, you want to look at your main attack pieces and make sure that you have ~5 orders you can reliably dump into one model if necessary and still accomplish the scenario.
I normally have four to five in US. One desperado in each pool A hardcase, sometimes two. warcor slips his way in there pretty often Devil Dog when I need a big beat stick.
In that case, I think you might be playing him wrong, as you shouldn't have any Irregular Orders. ;-)
To my mind the Irregulars in Ariadna never burden the list like they do in other factions. For one, we can get a lot of cheap regular orders, so if you compose your list well, you will not strugle finding enough orders to spend. Second: The irregulars that we have are very good on their own and dirt cheap. I always max out on Irmandinhos. Cause 8 point specialists with smoke grenades is a steal, and they can harass your opponent all on their own with essentially 2 orders a piece. I tend to get the Cateran T2 sniper who is mostly on ARO duty, so the order it generates isn't much of a big deal. And the Warcor is just pure magic with 3 points and a flash pulse. It has won and lost me battles simply blinding a essential unit or taking away precious orders from your opponent dealing with a journalist. Although there are a few irregulars which I always make sure that they have proficient regular orders to their disposal, so that they can really shine. The Dog Warrior and Antipodes come to mind. Since you want those puppies to get to the enemy as soon and fast as possible. The Antipodes to pick a nasty unit, like a TAG to just go and eat, while the Dog Warrior needs to rip up as many units as it can find, draining the opponents order pool. So I end up with around 5-6 irregular orders. Putting the Dog Warrior and/or Antipodes in the main 10 order group and putting the Irmandinhos, Warcor and Cateran in the second group.
I have been sticking with Caledonia lately and I have to run atleast 2 45ths when I do. then the Cateran T2 is a must. after that it varies on how I want to proceed but I will say minimum 3 for almost every list I build.