I've handled 4 a few different times before no problem. I much prefer 1-3 if they are young active (ahem high maintence drama queens) dogs though!
First when babysitting the Ridgeback boys for a couple months two years back... which was really easy because I stayed in their house so there were two fenced yards and good places to take them to run. Plus with two other dogs I could easily take one out for 1 on 1 without leaving Scout alone. I had Chico sleep in his crate because well when you've got 3 of 4 dogs who think you are the most valuable item in their existence... yeah. The girls slept in their crates or on the couch in the bedroom then anyway, but Lynley has seniority of Chicago, so yeah. I usually exercised Lily, Lynley, and Scout together, though each did also get one on one outings as well. Chico I exercised by himself, usually at night to avoid loose dogs coming up to us (he's not a fan). Everyone got a little training during one on one time and the girls were doing individual lessons.
The other big time handling four was when my ex visited last winter while I was fostering Spaz (now Zack) the little crackhead mini-aussie. Luckily his pit bull is one of the best dogs ever and super tolerant of the little jerk, lol. And of course I took the little booger when I home to my parent's on the weekend. He was such a douche to my parent's BC... I swear Will is a SAINT for putting up with his crap! They did very well all in all. Good bunch of dogs.
Its not the right time financially to add a third yet and I feel bad enough having a second dog with Lily around. Which is funny because before getting a second I was so sure she'd love it... well she does really well with it, but lets just say she'd much rather I be all hers.
Scout doesn't care because she's other dog co-dependant and must have a "pack" or she'll melt down with anxiety. Lily ... bless her awesome little husky heart wants me all to herself. She's done really, really well despite that. Especially considering the issue we have with Scout not being able to be left behind and her anxiety/reactivity have GREATLY changed where/how/etc. I take the dogs along. It is what it is. So sometimes Lily has to put her head down and pull like the sled dog she is because she doesn't like that my attention is divided. And thats okay because she is the princess.
I'm having a really, really hard time being impatient on getting a third. Which is really silly because I'm doing some pretty fun and awesome stuff with my two. And we've got a third on the weekend when we visit my parent's! THeir BC is just a peach of guy. Realistically I should wait until the girls are older both so they get their time in with me fairly as we're doing a LOT of training together. Scout may never trial because of her issues, but she has to have mental work to be really happy. She's just go, go, go... its really a shame she had to go through that stuff. Oh well, past is past! Anywho I apologize if I'm obnoxious ever talking about wanting a third dog or saying stuff like oh want! lol, I'm just being impatient! Its not quite time yet though!
The biggest perk to more than one is they can play and burn off crazy energy (yay sled dogs!). The biggest down side is hello prey drive magnification when together!
I am definitely not getting any more cats until both my currents have passed. Holy cat drama Batman!
There is a really adorable batch of kittens at the barn though... Oh its a good thing Missy and Scummy are such wenches regarding other cats!