Re: learning 2 arts at the same time
Two of my Aikido instructors are yoga instructors too. And another instructor have done Tai Chi, another trained in various martial arts too. In our dojo, there are Tai Chi classes too. It's really interesting, to see their perspective coming from different arts, because when I do a technique they would say... where you're open for an attack... etc. Sometimes the yoga instructor incorporates aikido principles to his yoga class... at least that's what I heard.
I think doing yoga, aikido and Tai Chi seems to complement each other nicely.
I'm in Ki-Aikido, I'm not sure what style you're in but this Tohei Sensei's principles has helped me to become more calm and at peace more than anything.