You definitely could be getting a better experience out of that combination. Hope this helps.
In my opinion, six-slotting Dark Regen as soon as possible is important. I generally go with one acc, one theft proc, at least two end reduction and one recharge, the last either end reduction or recharge. Once I hit level 30, if not before, I'll switch to one Touch of the Nictus acc/end/rech, one Theft of Essence acc/end/rech, three end/rech from other healing sets, and the Theft proc. This gives me decent accuracy and full end reduction and recharge. You want Dark Regen to be available as cheap as possible, as much as possible.
On a tank or even a low-level brute I'll often slot single-target attacks with one acc and one end for levelling, while slots are hard to find. AoEs are a good way to keep aggro and do some damage so those I tend to slot heavily, also with acc, end reduction, recharge, damage on a brute. I don't really bother with common damage IOs on a tank. When I can slot sets (and I do it early, 22-27 depending on set), damage will come. I don't care if I can't solo, because I have scrappers and brutes for that. (Also, once you get your build sorted out, you'll be able to solo, if slowly.)
I don't really bother putting end reduction in toggles that are cheap to run like your resists. 3 resist until I put a set of four IOs in. On DA I sometimes like Impervium Armor, which gives a bit of recovery and some max endurance, which also boosts your recovery (because you get a percentage of max per second).
Cloak of Fear is its own special problem. It's very expensive and doesn't hit. I run at least two acc/end from different fear sets just to make it manageable and not miss *all* the time. It's also the one I'll shut off if I'm having end problems but not dying.
There is no build I've ever heard of that involves skipping any of the resist toggles. Take them, slot them, love them. They're basically mandatory. Also, you're meant to leave the mezz protection on at all times.
DA isn't really a beginner set, but it's a very pretty set and if you can learn to work with it, it'll do amazing things. It pairs more easily in my opinion with Dark Melee, which gets you another big heal and an AoE end recovery attack. DA with a non-DM set just needs to work with whatever the mitigation options are in the secondary. In your case, it's Parry, which is I think melee and lethal defense. Won't help at all with people shooting non-lethal damage at you, but will be really solid vs things that stand and fight. Slot Parry with defense and recharge (and acc) and use it.
For stamina, two common IOs and two Performance Shifters: the plain end mod and the chance for endurance proc. That'll help. My DAs all just put Miracle in Health and call it good. For kb protection, 1-3 kb protection, Zephyrs in travel powers, Steadfast proc in a resistance power. Mine all hover so 1 kb protect is mostly enough, I get the other two later maybe.
I like a couple taunt/range/rech from different sets, or use a taunt/range or taunt/rech from the same set if you are after a bonus. More from a set if needed, but two usually seems sufficient. On DA, I like to dive into the group most of the time (my scrapper actually ports in), and then I'll taunt one of the group if it's big, or one of the guys standing nearby that hasn't gotten the picture yet. You should always be in the middle of a big fight, surrounded by foes, debuffing them, stunning them (Oppressive Gloom is pretty good), and if someone on your team is in trouble, they should be running to you if they can. Obviously you can and should taunt stray foes away from your team, but a DA that breaks away from a fight to go chase a runner can be asking for trouble once the fear/stun wears off the guys you were fighting. You have a lot less protection and opportunity to heal if you're getting aggro from outside melee range. I'm not sure why you can't hold aggro on a DA, though if you're turning off Death Shroud and not running Cloak of Fear, that might be the answer.
Depending on how set you are on absolutely having to have a) BS, b) DA, c) on a tank, I'd consider taking a couple days to try a couple of things. You happened to pick a fairly hard mode combination. DA has lots of potential, but a steeper learning curve than most, and it doesn't have particular synergy with BS. Doesn't mean it can't be fun and good, but I'm not surprised it's giving you trouble as your first DA. I also have an inv, and you're right, they play pretty differently. Inv tanks usually give you lots of friendly warning that they're in trouble, and there's lots of time to find some healing. Any sort of buff and they're pretty much golden, and if they run out of end, you can pretty much just taunt and let your end refill. DA *dies* if it runs out of end, because you can't heal.
BS/DA would make a pretty great scrapper or brute, if you wanted to keep the concept but not be responsible for the team. I've got a mace/DA brute that I don't really like tanking on. She's fun as damage and she can handle missions, but against an AV DA really works better with DM to back it up with a big heal, another fear, and end recovery. I don't think I'd get better results with the larger HP pool from a tank. I know DA/* *can* be good, but it's kind of hard mode, so I'd maybe see if you'd enjoy this character as a damage AT and another one as a tank, unless you're committed.