Need some advice on PvP (arena) gear and buildFollow

I need some advice in deciding between the two arena sets and possibly whatI should replace first. I also would appreciate advice in build taking into account my gear. Sorry for this being a little longwinded, just trying to give some info you may need.

Some background first: I already have a 70 rogue I raid extensively with, and after trying the different other classes I found that the warlock playstyle (as different as it is from rogue) was more appealing/enjoyable to me. After my husband started playing his own lock alt that he decided to keep as just a lvl 39 twink he became very excited about the idea of the two of us pvping together at 70 (me on my lock of course and him on his mage). So while I was leveling, he spent his time working on getting me the mats to get geared up once I hit 70. Thanks to him, when I dinged 70, I had full FSW, the girdle of ruination, and the battlecast set waiting for me. Since then I have filled in the other spots where I could.

The only raiding I do atm with this character is Kara and because of that, I have not gone completely for a pvp build. My character: http://www.wowarmory.com/character-sheet.xml?r=Kael%27thas&n=Marajade
(yes I know my +hit is pretty bad for raiding, I am slowly trying to create two sets 1 primarily for pvp and 1 primarily for raiding, atm my gear is more pvp oriented although I can switch a few items for more hit, like the spellstrike pants I seem to have logged out in, a different trinket, and a different offhand.)

Now, what I want to ask. Looking at the gear I have (switch out the spellstrike for battlecast and switch out the nexus-horn trinket for the insignia of the horde) am I geared more towards a destro build: 0/20/40 or? I am currently: http://www.wowarmory.com/character-talents.xml?r=Kael%27thas&n=Marajade I was trying to keep some raid use (my Kara group likes me to use this lock rather than my rogue on certain fights) yet still be viable for PvP. I have thought about staying where I am in the demo tree but switching the majority of the points that are currently in aff to the destro tree due to a major problem I have on Prince concerning my inability to use SB's due to me being too far away because of an infernal.

Last question, I am confused about the two merciless gladiator sets that I can start buying, they seem so much alike. And in this forum's opinion, what pieces would be best to start switching out.

Again, I apologize for the book, I have done a lot of research and reading, but am still somewhat confused unfortunately. Thank you for your patience.