First system

Due to constraints I have to put my speakers on a bookshelf with limited space behind them.

You have my sympathies.  Best of luck with that. 

You should audition the Sprout 100 and LS50 pairing before you commit. 
It will probably sound real good but I think you can get an equally good sound with speakers half its price when paired with the Sprout. The full potential of the LS50 will not be realized but it will give you room for future amp/preamp upgrades.

....also
i was looking into Super Tweeters recently. Specifically the Townshend Audio model. 
There was a forum or review I had read that stated above a particular frequency range( the Townshend are rated to 70khz) the sound is picked up through the eyes. I haven't done any further research on this and maybe total crap. But worth looking into. 

Hi Jacobo2u,
on bookshelves with little room between and behind says no rear firing ports. Form follows function. 

My my first thought when you mentioned not being able to hear above 13khz is vintage. There are quite a few excellent vintage speakers that roll of around 13 to 16khz. And they sound amazing. 
Something like a Goodmans maxim. The jbl D123 in a small enclosure would be nice as well. 

I had an original ps audio sprout. A couple of times really. It's very convenient and sound quality was good. I trust Paul McGowan and PS Audio so assume that the Sprout 100 will be even better. Another option in the PS Audio lineup is the trio line of downsized separate components. There are even some out there with Cullen Mod/Upgrades. 

if your looking for a nice all in one, had a Naim UnitiQute2 recently. Excellent piece of equipment. Don't let the low wpc output fool you. It's high current output can push some air around. 
Ive also been want to get my hands on a Cambridge Audio Minx Xi 

The combo would make perfect sense were it not for bookshelf placement of the speakers.

However the LS50’s do come with foam plugs for the ports and hopefully, someone will chime in about their use/sound.

FYI LS50’s are currently on sale KEF Direct/$999/pr.

This isn't directly answering your question, but i think I should write it, given the questions you have posed.
Given this is your first system, I believe you should audition as many speakers and systems, as possible.
If you are near dealers, go to as many as you can and listen to as many systems as you can so you can get an idea of what 'sound' you like.
If you aren't near dealers, make time to visit some-give them a heads up when you are coming so they can spend time with you.
(A good dealer will make time. He/she won't pressure you, sell you, judge you by your budget, or make you feel inferior-if they do walk out.
They should also allow you to listen above your budget, so you can see where the extra money goes).
Now, to answer your questions-
As far as power goes, get the speakers first, then work on the rest of the components-as system matching improves sound quality.
I wouldn't be concerned with hearing loss too much, I have it and tinnitus and can still appreciate my music.
My pick for a bookshelf would be a Vandersteen VLR and a pair of subs. I use HSU for my office and am impressed by the sound. If you have some floorspace, a pair of Vandy 1's would be my next choice.
You will get lots of recommendations here, so please try to listen in person first before you make a decision. It is time well spent and also a lot of fun.
Good luck!
Bob