I have 3, though I only personally own 2, my fiance owns 1 (well technically he owns 2 as I "sold" Vega to him, but she's still in my name and everything)
I do find it difficult to work all 3 in the winter as we have no indoor arena where I board.
When I only owned 2, I would work Vega and my fiance would work 2. It was actually nice having 1 green broke horse and 1 finished horse. Though when we found out Gem's arthritis, we stopped riding and really working him and just focused on getting him better. And then when he went lame and coliced, both of us focused in on getting Gem better and did little with Vega. When I was introducing him back to work, I'd only ride him for about 10-15 min (per the Vet's recommendation) and then I'd hop on Vega for more of a workout.
I lost a lot of confidence with her so I had put her up for sale and was looking for my next horse. My fiance was very hesitant to sell her as we would be splitting up Gem and Vega (they are very attached. He to her, more than she is attached to him), but we talked about it for a while and realized we'd be able to afford 3 horses.
I am thankful that I do have my fiance as he is eager to work with Gem again and to work with Vega, so I'll really only be working with 1.
If I was doing it by myself, I have no idea what I'd do, but I don't think I would be able to part with them. They have all taught me things and I know they still have things to teach me.
I've never just had 1 horse so I don't know how that is.
Sorry if this is long and a bit scattered.