I expect this will be a challenging MM build, but if you're 26, the worst part is behind you. Ninjas are squishy and TA doesn't offer much for protection, outside of the notion that "death is the ultimate mitigation".
Flash - wouldn't worry too much about recharge. Base is 15 seconds and effects last a minute. Good for Cloud Senses, if you want to get that set.
Glue - affects everyone on the patch. Dmg proc would be cool.
Acid - the -resist proc goes nicely in here, to make you a -res debuffing machine (proc + acid + disruption). Don't bother with damage.
PGA - I'm seemingly one of the few proponents of this power. -Dmg is one of your few "safety" abilities.
OSA - this is the opposite of Acid, you should definitely enhance the damage here, it's glorious when lit. The double edge sword for Ninjas though (no pun intended) is that they won't go onto the patch while it's lit.
EMP - slot this as a hold, similar to what you do for Ice.
Other general comments, on what I'd do for a Ninja/TA:
Get Assault - with all the -Res, you'll get bonus damage from Assault based on the multiplicitive relationship of dmg and resistance.
Get Medicine - as mentioned above, Ninja are squishy and TA doesn't do much to protect them.
You didn't seem to have any questions about Ninjas, but Smoke Flash is very very nice.
Global = Hedgefund (or some derivation thereof)
Thanks. Yeah, I've kind of gotten the hang of Ninjas (and already have Medicine. It became an obvious early pick. 
) Just have to keep a leash on them so they don't go too crazy. Assault's a good point, and should be easy to work into the build (what else am I going to take, snap shot? Heh.)
Thanks again!
Wanted: Origin centric story arcs.
If you've only played an AT once (one set combo) and "hate" it - don't give up. Roll a different combo. It may just be those sets not clicking for you.
Deacon covered it all pretty much. For your APP choice, if you go with field mastery, any energy damage attacks will set the OSA on fire just like any fire attacks. I have a Nin/TA at lvl 37 now, and that's the plan for him. EMP arrow, fr the record, can be slotted with End Mod as well if you want to turn it into a sapping arrow.
I'm working, on and off, on a Nin/TA build. Yes, I've heard TA isn't the best and Nin is squishy, but it's been fun so far (except for scrapyarders. Stupid demolitionists.)
With the upcoming inherent stamina, too, I'm looking at the build and thinking it's already slot-light. And this set doesn't seem to have a lot of set-worthy slotting (sleep? Really?) to where this almost seems fine on common IOs right now.
But I want to play around a bit. No expensive builds, this is a very casually played character. I do want to see what "interesting" things can be done with it. So I'm wondering what people tend to go for with /TA MMs.
This is kind of what I have in mind. (Yes, I *am* 26, but I'm looking at where to assign slots in the future aside from pets.)
Entangling arrow - Stacks on its own pretty well, from what I see. I'm tempted to go for accuracy and maybe a little recharge, and throwing in a Trap of the Hunter proc just for laughs.
Flash arrow - Acc and recharge? I don't think I want to put the procs in this since, if I remember right, those will be enough to cause aggro (getting rid of one of the things I use it for.)
Glue Arrow - Just recharge, mostly? (Another "proc for laughs" if I can snag one from Impeded Swiftness. Does it affect just the target or everyone on the patch?)
Ice Arrow - This is getting slotted up, hopefully enough to stack with itself and keep something held. Rech, Acc, Hold - kind of classic controller slotting. Probably the first power I keep planning to really *invest* in.
Poison Gas Arrow - Just recharge, I know. Probably not adding any slots.
Acid Arrow - OK. First real question. Do I want to use this mostly as Defense Debuff or damage? Or mix both (with, perhaps, a Lady Grey proc?)
Disruption arrow - No sets for it, so recharge is pretty straightforward (and why don't we get resistance debuff sets?)
Oil Slick Arrow - Again, go for a Targeted AOE set (Posi's I'd assume) or the debuff? Does the PosiProc see the Oil Slick "pet" as a legitimate target as well?
EMP Arrow - No idea. It's a little ways away.
FWIW, I'm considering Heat mastery (skipping the PPPs for the APP) - just to self light Oil Slick. However, there's no shield in it as I look at the wiki. Will Field or Charge work just as well? (Yeah, I've never had a /TA anything to play with Oil Slick with.)
Really, as far as slotting and enhancing, /TA looks cheap (a lot of places to "just use commons and forget it.") After the pets get slotted, I've got a ton of leftover slots it seems like, which is a nice difference from some of my other characters. Just looking for comments (other than "lol reroll," not going to happen) and suggestions.
Wanted: Origin centric story arcs.
If you've only played an AT once (one set combo) and "hate" it - don't give up. Roll a different combo. It may just be those sets not clicking for you.