Yes 18-20k is normal quotation for Invisalign depending on your case thou. sometimes can be cheaper.

Invisalign is clear braces where you dont have to have any brackets on your teeth, with some help of attachments and the aligner, your teeth can be moved and achieve the final result as braces too.

Benefit of invisalign would be more comfortable, removable and doesnt interfere with eating, easier to clean and maintain hygiene.

As for timing, not significant studies show that invisalign is faster but most dentist feedback says that it is. Even so it wont differ by a lot.

If you have the $$$, and want a more comfortable experience, go for Invisalign.

This OPG x-ray is not sufficient for me to provide you with advice on your treatment.

But one thing is for sure, you should remove the tooth that is impacted under the other teeth, they risk causing problems in future and may interfere with your tooth movement.

Damon Clear is basically ceramic, functions the same with regular Damon (stainless steel).

Ceramics will have higher friction with the wires that will slow down tooth movement therefore slower result. But the end result would still be the same. Just longer time.

Go for regular Damon if possible if you're ok with the metal showing, unless you really must look good even with the braces then you can opt for Damon clear, but be prepared for longer treatment time and increased cost too.

ah basically one of the premolars is stuck under the tooth as there is not enough space to come out.

You have to undergo a minor surgery to remove the hidden tooth. but prior to that, your dentist would probably take a 3D x-ray to ascertain the position of the tooth to plan for the removal approach.

haha. its a minor surgery, you can do it with local anesthesia, meaning only numbing that area, you dont have to go through a full body numb. But choice is up to you.

I'll give you a PM on recommendation. Cheers