Perhaps a utility mine.. like tractor beam. Dont know of any other really.
Breen cluster torpedo, there's a shield draining mine from the lobi store, bioneural warhead is a bit lulzy.
I wouldn't use overload if I was running just the one beam array in the back; I'd use subsystem targeting. Yeah, they've got cooldowns, and even shared cooldowns, but 15s on the shared cooldown isn't that bad.
I already run into a version of this problem with my FTER, which has an extra ensign tactical slot that I don't need; I currently run 3xTT1, which gives me a lone copy of TT to use on the odd occasion I want to use it outside of chaining it with APB and CRF (usually in a support capacity, though sometimes in conjunction with evasive maneuvers).
I bought the whole 5000 zen package for the Kumari 3 set and it's probably one of the best zen purchases I've ever made. The Kumari is a huge blast to fly. It is very fun, has a lot of fiyapowa potential, and contrary to a lot of people's assumptions isn't necessarily squishy. Keep in mind that plenty of people do not know how to build their ships or pick the right active doffs or train the right boff or pick the right gear to keep their ship alive.
Since you only have 2500 zen, it's hard to pick the right one. What I can tell you is this: the tac version, the Kumari itself, has a console that acts like a Guramba javelin. Unlike the Guramba you don't need to go into siege mode. The Kumari's overload deals a nice amount of damage: I scored a crit hit of about 122,000 damage. The wing cannon pet console on the Charal I think, and they do less damage than a DHC but they do damage and assist you. The other Kumari version has a console that does a bit of damage to an NPC's shields and weakens their shields by 25% for about 15 seconds or so, which isn't really as good as the other consoles imo. 2/3 of the set nets you 10% accuracy overall across the board, and 3/3 of the set lets your wing cannon pets mirror your wing cannon abilities.
I'm a tac captain and I've used the tac Kumari and the Charal in a lot of elite STFs ever since the ship came out. It isn't as glass as some people might think, but obviously it's not going to tank as well as a carrier. I've experimented with having 1 wing cannon + 4 DHCs on my Charal (no torps) which works in ESTFs, and I've also played around with my tac Kumari that has a torpedo launcher instead of a fourth DHC. It also works.
Basically it depends on what you like to fly, pretty much. The Charal has a better ability to tank than the tac Kumari, but the tac Kumari has more firepower, and can still survive in estfs. You can easily do probe duty and solo transformers with a tac Kumari without it dying. Cubes die too fast to a monster like it. If you're a skilled pilot, you can also tank a tac cube for a while. It just depends on how fast you are and whether you remember to hit your buffs.
Turn your Brace for Impact into a makeshift emergency heal/resistance buff. I use the following boffs (all very rare): 1 vs Borg space warfare specialist, 3 shield distribution, 1 hazard engineer. This makes brace for impact have 3x 50% chance of healing 2,251 shields per facing, as well as giving you a resistance buff. This has saved my ship on various occasions to get an instant big heal. This is enormously helpful not only with a tac Kumari but with the other versions as well.
Consider "tanky" gear. I'm using an Aegis set on my Kumari before I get Omega gear (I rolled an Andorian as soon as Kumaris came out). It costs like 5-6 mil total for all 3 Aegis pieces but it's a big help to keeping you alive. On my tac Kumari I'm using 2 neutroniums and 1 field generator (I have all 3 Andorian consoles but I only use the wing cannons + overload). On my Charal I use a second field generator.
My boff ability on my Charal is as follows: TT1/CRF1/APO1/APO3 - TT1/CSV1/CRF2 - PH1/HE2 - EPtW1 - EPtS1/RSP2
On my tac Kumari I have no EPtW or RSP2 which is where Brace for Impact on steroids comes in handy. The extra tac slot lets me use torp spread 1 and cannon rapid fire 1, and I simply change CRF2 to torp high yield 3 for my torp launcher. This helps enormously against cubes.
Not only do all versions of the Kumari work very well in elite STFs but the other space pves as well, like Minefield, Azure, and so on. I can pretty much guarantee you that if you use the tac Kumari, you will get the top damage/rewards in Minefield.
Sorry if this post is too long for you to read but this is all stuff I've learned on my own and with a friend of mine who flies a tac Kumari with a tac captain as well. We fairly regularly do elite STFs together. We don't die any more or less than people in carriers and cruisers and other escorts. The Kumari, any version of Kumari, is totally viable in any PVE. It only depends on who is piloting it.
One thing I should add: do not mix and match your weapons. Beams and beam abilities do less damage than DHCs and cannon abilities. Beams have bigger firing arcs, but if you're flying an escort you are already fast and maneuverable to keep something in your forward firing arc. Don't use beams on an escort, it needlessly lowers your DPS.