We had four dogs at two points in time. We had Samwise (Border Collie x Lab), Oliver (Lab mix), Layla (Boxer), and Georgia (Boxer). Three were fosters. It really didn't seem like it was too hectic. In fact, it was a lot of fun working with all of them and taking them to the park, and rollerblading with four dogs at once.
At the other point, we had Alaska (Boxer), Georgia (Boxer), Suzie Q (Dachshund), and Buddy (Pit bull). I agree with the small dogs being more work, despite their size. Suzie Q was a yappy, yippy, picky, bratty big weiner. But they all did well together, and we loved them all. It's always more work - especially with two of those dogs being fosters, both with problems that needed working on. It's a lot of fun, and I say go for it!
At another point, we had six. We had Georgia (Boxer), Elly (Labrador), Molly (Labrador mix), Oliver (Labrador mix), Bailey (Labrador) and Layla (Boxer). That was a ton of fun, and believe it or not - it wasn't much work! And I was the only one who would work with them and care for them. With any number of dogs, you have to be in control, especially with four or more- or it can be really stressfull. I had them out playing 4-6 hours a day. In the summer I would spend all day with the dogs, and on school days they'd be in the kennel (which had to be pad locked, because trouble maker Molly learned how to open any kind of door) for up to 7 hours, and as soon as I got home we'd be out playing, no matter what the weather for usually around 4 hours. And then even after that, the dogs would stay outside playing. We live on 2 acres, so it wasn't an issue leaving them outside. As long as they were exercised and their minds were occupied and as long as they were extremely tired by the time they came inside - all was under control.
EDIT: I just saw that you adopted him!
He's so tiny. YAY! Congratulations!
He can't be too much trouble, can he?
