6. About using your current stem and not a T stem. It is possible, no problem to make it fit but:

I kept searching for old posts and found a Bikeforums post about this. You need to take som time to look at this post, there are a lot of pictures. search for: Aber Hallo or Litepro Stem Ekstender?

In that thread they say that maybe the quick release top (like you have on your bike) is not strong enough in the long run to hold the handlebar.

I find that to be a bit strange becouse if it can hold a handlebar it can aso hold the handlebar extender unless you are an extremely strong rider and pull on the handlebar a lot.

I have seen no warnings from peopel selling the extenders not to use them with quick release.

Also you can buy a new top for the adjustable handlebar and I would think also a top with two bolts instead of a quick release if you are worryed about strenght.

In the BF thread about Aber Hallo and Litepro there are other options discussed also. You can cut of the top of the handlebar and use an adjustable ahead or quill stem that may be in the shop already so no need to buy online.

I think you should first choose a shop (a independed bikeshop, not a chain store) and talk with them about what they can do.

Print out the thread I mentioned (or bring a computer to the shop) and ask in 2-3 shops what they would suggest.

You can also e.mail them with a link.