Well, if ya already have 2 inside....1 outside shouldn't present a problem.
Porter and Keagan aren't strictly inside cats.
When we got them, as kittens, at two different shelters (they are almost exactly the same age), we agreed that we would keep them inside. That was 9-1/2 years ago, and we lived in a high population area. We agreed, for their protection.
When we moved here, we were way out in the country and had a fenced back yard. They REALLY wanted to go outside, so we figured, "Why not???" Both cats stayed in the back yard and enjoyed chasing insects & laying in the grass, soaking up the sun.
When we fenced in the side yard, we removed the backyard gate, which gave them a bigger fenced area to roam. They did figure out a way to go under the workshop, which is on pier & beam. So, occasionally the do get out to the front yard. But, they usually come back after a short while.
Keagan is a big, short hair cat, has always been 22 to 24 pounds, with lots of padding. We feed everyone the same food & same amount. Porter is our Maine Coon mix, who has always been 14 to 15 pounds, on the slender side (you could feel his ribs).
Since we have been letting them out to roam, within the fenced area, I recently noticed that Keagan actually had a waist - which he hasn't had since he was a kitten. So I weighed the boys a couple weeks back. Keagan had lost a whopping 4 pounds, and now weighs 18 pounds. Porter has lost two pounds and weighs 12 pounds. Now I would say he is on the "slender side". So letting them outside has been very healthy for them!
Talking about weights, I was curious about Butterscotch. When I went out to weigh him, he wasn't there. So, I called him, and he came running.

He knows his name!!!
I had a box on my kitchen scale. At first he didn't like the idea of going in the box. But I helped him sit down & he curled up, in the box, and purred!

What a sweetie!
So, he weighs 7 lbs 2 oz. He's just an itty, bitty thing, compared to our two big boys!
After I weighed him, DH sat in the porch chair & Butterscotch jumped in his lap and started "making muffins" on his leg!