Re: Complementary Aikido Styles
Aikido styles really need a family tree of sorts to make even basic sense of the variety.
That being said, I'd cautious about trying to do too much at once. I tried doing Renshinkai (Yoshinkan-based) at the same time as my regular Aikikai practice and ended up injured when I tried to do forward ukemi in reverse to what I knew. Also having to focus doubly as hard every time I went to train for simple things like which foot to put forward made it less than relaxing to practice.
If I had the time to practice anything else, it'd probably be Tai Chi or yoga.