Hi quiggers!
Welcome to sailing, wish you many happy days on the water. GL is right, the O'Day Daysailer is a great family boat, and a great boat to learn on. That is exactly what George O'Day developed it for, 60 years ago! I took a quick look at used Rumba prices on Craigslist, and I can assure you that you can find a used DS for the same $1100-1700 range. Obviously, everyone on this forum is pre-disposed to recommend a DS, so I'll just give you my opinion on choices for your first boat, fwiw.....
I think it boils down to two main points: 1) A boat you can sit IN, rather than on and 2) A boat that you can grow along with your skills. What I mean by in/on is that you just have a lot more space to move around and places to sit if you want to get "out of the action" (tired kids!) on a Daysailer. On a small dinghy, such as the Rumba, you and everyone aboard have to sit in exactly the right place or it flips. The Daysailer is way more forgiving. It's the difference between riding a scooter vs riding in a small car. Tired kids? Go lie down in the cuddy. Want to bring a cooler? Stick it in the cuddy. Want to lie down? Lie down on the seats. Etc. The Daysailer is large enough to give you that freedom, without losing the advantages of a dinghy (light, maneuverable, beachable, easy to rig). Likewise, as your skills grow, you can add a spinnaker, extra sail controls, etc. The Rumba is what it is, pretty much set in stone. IMHO, you'll quickly outgrow it.
Now, with that being said, any of the larger dinghies has the same advantages as the DS. Last weekend I was helping out a newbie on an American 14.6, nice boat! These types of boat are relatively cheap and easy to handle. Big advantage of the DS is the cuddy - you have a "Below decks" space without all the weight/expense of a keelboat. Honestly, it's about as much space and headroom as being underneath a dining room table, but it beats having nothing at all. O'Day put it on specifically for family-friendliness. Big disadvantage of the DS is that it's 550lbs and you'll need to think a bit as you rig it and move it on/off trailer. Something like the Rumba, you can rig with one hand and then hop on and go. Again, pretty much like a scooter vs a car.
If you had no sailing experience at all, I could see getting the Rumba and then switching to a large dinghy next year. But you already know windsurfing - the Rumba is a windsurfer you can sit on instead of stand on, so you wont be learning much anything new. Go for the bigger boat

Tom