Re: learning 2 arts at the same time
I dont think there is anything wrong with cross training as long as you have enough of a concept of both in order to seperate the 2 or however many. I would suggest taking Aikido for a little longer before starting though. Aikido can almost act like the building blocks for other martial arts too. It really helps with speed , foot movement, reflexes, timing, agilitly, and so on. Not too say that aikido isnt good enough to just do it ( believe me i've done it for 7 1/2 years , it is good) But i think doing aikido first teaches you what most martial arts are about and it will make doing other martial arts in the future a whole lot easier.
Also ask your sensei about other arts before switching to one. I told my sensei that i had started doing shaolin last year and he goes "You're doing shaolin? I love shaolin , i had a brown belt in it when i was a teenager." And he also has a black belt in Judo and he's studied a handful of other arts too. Surprisingly enough , his favorite is aikido. So talk to your sensei , he may know alot more than u think.
I think cross training is great , you just have to pick the right time to start doing it. But then again like Eric said, "some can handle it, and others cant." Very true.