Compliments on a nicely presented query - refreshing to get all the core details right up front.
Personally I see 4 core keepers Horton, Nash, Gustavsson and Kaberle. After that I think Roy, Booth, Gomez, Gagner and Letang would be my considerations. Keeping Booth scares me a little but keeping 3C doesn't really seem too appealing either. You have nice depth at D but keeping more than 2 also isn't that desirable. Byfulgien normally wouldn't be a keeper in this league but I wonder if your hand is forced a little because you really want to keep some balance.
I am talking myself into keeping Roy, Gomez, Byfulgien and Letang as your other skaters - unless you are like me and are prepared to take 1 risk and then I would substitute Booth for Byf and pray.
I think when you only keep 8 players the answer to the question of "where do I need to improve?" is quite simple - everywhere. I think you have only 2 ironclad keepers here in Nash and Kaberle for a league your size. Next year going into the draft you sure would like to have better players at each position to protect.
Obviously with so few protected, you are going to have some real opportunity to grab talent in your first draft - do your homework, make a plan, stick with it. Better wingers would be my priority and then a goalie upgrade. I think you already see that - so draft away lad.