That's a deep roster and there are multiple good teams you could make with that. I'm going to assume all toons are max geared? If not, focus on that.
Here's what I would suggest to get you focused in:
1. don't try to min/max right now. I actually lean towards the min/max camp, but with the impending level cap, don't focus on that right now, because a lot will likely change with the raised level cap in terms of whats "the best
2. Think of how you want to fight in arena's (aoe, tank plus glass cannons, 1 vs 2 vs no healer) and start there.
3. Once you know what type of team you want to build, I would lean towards toons that are going to be easiest to star up ie-is there a strong team, that matches your preferred build that has one toon you can level from GW, one from arena shipments, one from cantina shipments allowing you to star up quicker? now if you're willing to continue pumping money into it, you can just buy chromium packs until you've got 5 good toons 7*, but I'm assuming you're not wanting to do that.
4. Once you have figured out which toons match your playing style and can be leveled up, make sure they are all max geared if you haven't already, and of course max level as you level up.
5. Grind away towards 7* on these toons and start running them in arena's. This is just a starting point. Down the road you may decide another toon works better in your line up and you just have to eat the lost time and resources on the toon you replace. I think this is nearly inevitable as play styles and preferences change and of course patches, cap raises, etc can drastically effect your team. Don't sweat it.
Now, I suggest you use above to create the team that's the most fun for you to play. But if you want a specific recommendation:
I'm 60, top 10 every night, top 5 most nights and finished #1 the last 3 nights (keep in mind, with the current metrics, that has more to do with the timing of my arena games than skill or even team build). I personally run:
6* Sid (Leader)
6* Lumi
6* JC
5* Dooku
5* Fett
I like the team and it works well.
I am currently working on a team that will consist of
Sid (Leader)
Poe
Dooku
IG88
Fett (I want this slot to be vader so badly, but with him stuck at 4*, I think the team will do better with Fett
But am working on getting Poe to 4* and IG88 to 5* before I try this (Sid will be 7* in the morning). If Poe cant provide enough cover for the glass cannons I may very it up. Another version of this would have Leia and FOTP. I don't like Leia due to limitations in leveling her up. FOTP could be sub'd in but he's also difficult to level up and the various stuns, debuffs etc this build gives me. Finally i'm also in the process of unlocking Ren but haven't decided how i'm going to work him in yet.
One last note, I don't have Ben and Lando, but certainly they can be effective on an arena team, but you should decide if you're willing to commit the resources to level them up down the road.
Just my take on you're question and it's worth precisely what you paid for it, but I hope that helps ;P.