Re: Judo first?
I've been in a handful of physical confrontations and it was my Judo background (and a little luck) that kept me from incurring serious injuries. I love the training I do now, but when push comes to shove my first instinct is to get inside, grab some clothes and send ass over head.
If you're end goal is to practice Aikido, just start training. If you feel like something is missing then cross-train in another art.