Re: Judo first?
I was in judo for 8 years, rather intensively. The senior guys in the two dojo I practiced in, in Vancouver, had all spent significant time living and training in Japan in the 60s. Doug Rogers at UBC was a fairly recent Olympic silver medalist and a godan, G Thom was a sandan who'd been open weight champion of south africa several times, but was only 70 kg, D. Jinks - yondan Irishman who'd been in japan for many years... I took up Aikido at age 40.
Ukemi (the falls and so on) in judo is a matter of trying not to land on your back and learning to do that while not getting hurt and while the other guy is actively trying to make sure you land on your back. Ukemi in Aikido is most often being off-balanced and directed to the ground but you have to look out for yourself and not land on a corner (e.g., your shoulder) because after the throw, Nage tends to let you fly so he or she can attend to another attacker. i.e., Ukemi in Aikido is more about not getting hurt, Ukemi in judo is more about surviving and not giving up a point. (this is MY point of view, others may differ)
So. It depends. Judo is about competition, in the long run, and has a bunch of rules. Until you're going for higher dan grades, you don't often practice defense against kicks, punches, weapons attacks. You don't learn to protect your face against a punch - because the sport doesn't allow it. You get tough from the "safe" combat. "Safe" because you learn to take a fall, you learn to throw, but it doesn't include full-contact striking or weapons. You learn "safe" grappling. "Safe" because you learn techniques that are aimed at competition - strangulations (with rules) - hold-downs, escapes from hold downs, and elbow locks.
Few Aikido dojo include ground grappling. However you can (depending on the dojo and the sensei) learn practical defense against strikes, weapons, and get lots and lots of physical fitness. (hint - most of the physical fitness comes from ukemi and getting back up). Depending on the instructor, you can spend a lot of time practicing, or you can spend a lot of time watching the instructor (sensei) demonstrate and mumble.
I won't return to judo. This old body can't take it. With Aikido I can plead "old" and slow down - I do it more for exercise these days than the "martial" aspect. Depending on YOUR age and physical literacy, you may benefit from an "old school" dojo that has a lot of bashing around, or you may benefit from a more placid dojo that is a little more philosophy than flying bodies.
If you're young - it wouldn't hurt your Aikido very much if you spend a little time in judo, but remember that they're very different, even though related.