Honestly, with cats, adding to the family (wrt adding other cats) has the potential to be messy (especially if they are indoor only and are sharing a fixed territory - indoor/outdoor cats can at least part ways at the cat flap). It also can have the potential to go really well (Sonic and Jakes ADORE one another and usually sleep curled up together), but it's a bit of a gamble every time. I never ever want to relive the stress of adding new felines to the established adult feline indoor-only family, if at any point in future after this lot are no longer with us
I decide to have multiple cats I will get them all at around the same time when they are all between the ages of 3 to 6 months old.
Something to bear in mind is that when left to their own devices in a feral environment, females of reproductive age do not tolerate having overlapping territory with another mature female - and they can fight and spray just as well as any male cat. Male territories tend to be larger but will overlap with one another at the fringes and also overlap with female territories. I would suggest that if you wanted to introduce another cat, go for either an older neutered male with an easygoing personality who is used to sharing space with a female cat, or a male kitten that is fairly laid back and will do what he's told by Breeze. I'd avoid 'highly strung' or high energy/dominant personality breeds (Rexes/Oris/Siams/Bengals), and also very shy/nervous breeds (Russian Blue etc) - you'll want a cat that is neither wanting to take top spot, nor too likely to be bullied. Another MC, or a Ragdoll or NFC might be good, the latter two breeds are known for being easygoing in multicat households or with other pets.
Probably goes without saying that the first priority should be existing pets - yes it's disruptive to a kitten to return it to the breeder/shelter if it all goes pear-shaped, but it's worse to keep it if it's going to make either it or your existing cat's life a misery for the next however many years.