Answers

Hard to tell for sure without a close look, but the roofing / waterproofing material looks like TPO, a single-ply roofing membrance.  It is not made for direct traffic, so appears someone has installed rubber pavers over it to protect the membrane.  Not an unusual application.  The membrane should have positive drainage to what appears to be scuppers, and any water falling on that balcony wants to be able to freely drain - meaning, any pavers installed should have a means of drainage on the underside.  Appears to me that these rubber walkpads really do not.

Have a professional roofer /waterproofing company take a look and work with you toward a solution.

It’s most likely a common wall. I’m extremely worried about neighbors hearing extremely private noises.

The least expensive option is going to be to create white noise.

Otherwise, you'll need some type of sound insulation and dense pack cellulose might be able to be retrofitted into the wall cavity. But determining your level of performance expectation is the hard part. How perfect do you expect it to be? Is this a common wall to another unit, or all enclosed within yours? It makes a difference.

Spray insulation foam close cell.

Rockwoll Insulation is a great way stop reduce sound.

I have seen a lot of great DIY carpenter bee traps that fill up with bees. I have friends that say the traps keep them out of the house. 

https://www.pinterest.com/explore/carpenter-bee-trap/

I believe Home Depot has some aerosol products that can nearly reach 40 ft, but not positive.

There is a bee spray you can mix in a pump up and reach the higher carpenter bee holes. This worked for me.

Bee spray typicaqlly has a really far reach or an exterminator. 

Most hardwood floors can be cleaned easily with a microfiber mop and a natural cleaner such as Mohawk's Floorcare Essentials Hardwood and Laminate Cleaner. It is all natural, works great and doesnt leave a hazy film on the floor. As with any product you use, make sure you test it first in a small area.

Vinegar deluted with water is safe and works well.  Bona is another product that works.  Do NOT steam clean real wood floors with a steamer or use pine sol!!

A tankless water heater can certainly be installed in a condominium - similar to any other structure. The easiest model is one that mounts externally - typically near the highest use of hot water or midway between multiple usage points. If there is some distance between the use locations, you can also install a D'mand pump to "call" the hot water so you are not wasting water waiting for the hot water to arrive. If you install a unit on the interior of your unit, e.g., in the previous water heater closet, the unit will require venting.  And - FYI - one reason people love to install an on-demand is that you can actually repurpose a former water heater closet creating more useable space in your condo.   One last piece of important information, you will need to check the size of your incoming water line.  Typically water lines are 3/4 inches in diameter.  On-demand units require incoming water lines of one inch.  So you may need to upgrade your plumbing to accomodate the increased size of your incoming water lines.  I hope that helps.

Yes you can. However every condominium association has its owns rules and regulations.