For question 1 – default sidebar for properties submitted is primary sidebar. This is hardcoded I am afraid and would have to be edited in the code. Maybe we can give a direction to what file to modify. I will ask my colleagues to take a look.
For question 2- you can modify the file using this forum instructions http://wpestate.org/forums/topic/how-to-make-small-slider-default-in-user-submission/
You can remove the full width slider in the code as well.
For question 3 – I don’t know of any option that could allow the SEO YOAST plugin to work in front end submission. You can ask them as well, but I don’t believe this option exists.