Poodle as dog #3?

Howdy from Texas, ya'll. I have two dogs, Bailey, a rescued male Maltese and Harley, a 4 year old male Rottweiler. Bailey is getting up there in years and Harley is finally 100% mature, so I'm thinking now would be a good time to add another dog.

I feel very torn between getting another big dog or another little one. Big dogs are awesome. If I went with that option, Harley would have a buddy to romp with. Would a Standard Poodle be able to handle that? Harley is extremely well behaved and loves other dogs. He is very submissive for a Rottie, so I'm not worried about dog aggression at all. He is a BIG boy though and if I got another large dog, I wouldn't want it to get accidentally hurt. There are a few large breeds that I really like but dog aggression (from the new dog) and prey drive (in addition to the Malt, I have four cats) are concerns. I also don't want a huge dog. Having a dog as big as Harley makes traveling quite difficult, his crate takes up a lot of room and he barely fits in the back seat of my car.

I've always loved the standards. My SIL is a groomer and recently got her first one. My bro and SIL are bringing him to visit for Thanksgiving and I'm so excited. She also has a friend, her mentor, that has a beautiful black standard boy. Both dogs live with other animals and small children with no problem.

I groom my Maltese myself, so I feel kind of prepared for a poodle's grooming needs. What kind of energy level do the Standards have? My main reason for picking a Rottweiler was their energy level. I wanted a large dog that would have the stamina for long walks/hikes, but was calm indoors. Harley fits that to a T. He is sleeping (snoring) at my feet while I'm typing this, LOL. He loves playing in the yard and going for walks, but know how to behave in the house.