I just went back up to 3 -- 2 yorkies and 1 Jack Russell (the JR is really my son's & he is off at college). I think 3 works well for us. My other yorkie Ben, was very standoffish at first, but Annie was persistent and they are already playing and sleeping on each other. I would not recommend a male though, since your male is marking.
My male, Ben, never marked even after being dad of a litter. Then I wound up having a male as last puppy left of his second litter. Long story short, I kept him for a few months. I had not found the right person and I thought about keeping the male puppy (I named him Rocky). It started off with them trying to out-mark each other. That itself was pretty bad (I even got half the house tiled to try to alleviate the problem $$$). But they did not get along either and the fighting was really escalating when my DIL told me her best friend (who I had met & liked) would really like to have him. I wound up giving her a really good deal & was very honest about the marking. She took him, has him using a doggy door, no marking and he gets along great with my DIL's poodles they often visit.
Some here on YT, have gotten a second male and made it work. But I cannot recommend that. My Annie though, has been a delightful addition to our family and even Ben has warmed to her and is more than accepting her -- he really enjoys her. I forgot to mention Candy, our Jack Russell, loves everyone and gets along great -- she thinks she is a yorkie as I have always had yorkies with her around. She mothers them all.
So my ABCs are doing great!
Other than that just consider the financial aspect and be sure you have a few thousand set aside or insurance/care credit car for vet bills -- just in case.