This is the tablet forum, not the TV forum, so I'm locking this thread. But not without a few answers.

1. Sound of smart TV's is mediocre at best. Consider buying a sound bar.
2. OLE is considered better than LCD.
3. Prices vary per shop. So this part of your question can't be answered.
4. All specs are available on Samsungs site. A lot also on our site at https://www.cnet.com/topics/tvs/products. Many webshops have specs and compare-options also.