I'll try a short response.
1. One hand up, pointing upwards with one hand down, pointing downwards.
Christian Tissier does this pose sometimes. His Teacher Yamaguchi also did it.
It can be a very good position of zanshin. But if you force it, it will hinder your technique. It will often be the result of doing a technique totally relaxed.
In our Training we deliberately try not to use it!
The atari movements of Endo have something of those push tests. And we do some other things which remind me of the push-tests of Ueshiba.
We are not doing ki-Tests like ki aikido. It's different.
My teacher is the German shibucho of the Sugino dojo.
Christian Tissier teaches the derivate of Kashima shin ryu he learns from Inaba Sensei. Who also teaches in Germay.
There is a lot of koryu weapons touching our aikido.
Tissier himself was activ in kickboxing, which is very popular in France. And trains with karateka of the national team.
Well: We often mix up with people of other arts or sports. We have seminars or we train together and have people of other arts or sports in our regular training.
No insular existence at all.