Although it gets a lot of heals, the key power is actually fortitude, which you want to keep on as many people as you can. Without the defense from fortitude, people die too quickly for heals to save them; the more people are constantly under fort, the better your support power is. Therefore you need recharge, lots of it.
As a rule of thumb an SO build ought to be able to fort 2-3 people, a cheap IO build 4-5, and a top-tier build 6-7. An IO build should also strive to keep Adrenaline boost constantly going on one person.
Empathy doesn't build for defense well since it is slot intensive and does not self-buff defense, resistance or recharge. A related problem is that support emps tend to get hit by a lot of aoe damage, and aoe defense is hard to build for without compromising recharge. You will have to live with being squishy.
I strongly recommend taking Maneuvers. Maneuvers + Fort is almost 29 defense to all, including psi. An SR scrapper with SOs slotted only gets about 31 def to all.
You're not really getting a lot out of power mastery. Total focus is dangerous to use since it has a very long animation and the damage is poor. The only notable power is power build up, which increases the defense given by fort, but you're not taking that. I recommend psi mastery instead, which gives you a good ST hold, Dominate. It's also a very good attack.
This is a cheap (no purple/pvpIO) nearly-permahasten build that ought to be able to fort 5-6 people and keep AB permanent on 1 player. The endmod in AB is to push its recovery over +1000%, which defeats the -1000% endurance debuff that crashing nukes give. There's an endredux in recovery aura because the high casting cost (26 end unslotted) sometimes means you don't have enough end to cast it if you're running low. With this build you should hover far from melee and blast cautiously.
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If you're going to 5-slot heals, Doctored Wounds or Regenerative Tissue is the way to go. There just aren't any good defense bonuses in heal sets at the 5 slot level, so might as well go for recharge. If maxhp is what you're after, 3 slots is sufficient.
I'm sure other posters will chime in with excellent Empathy advice, so I'll talk about the other half of your build.
Psychic Scream and Psionic Tornado are excellent mitigation powers. Take them early, slot them generously. They can floor enemies' recharge rates reliably and with good duration. Positron's Blast, however, simply doesn't have the recharge bonus to pull it off. Go for frankenslotting instead. For Psychic Scream, some variation on 2xCentriole, 2xDmg/Acc/End, 2xRech, is the way to go. For Psionic Tornado, range slotting is unnecessary, so you can add a Rech IO to round out a Positron's Blast set, if you prefer. Take slots from Clear Mind, Rez, and Conserve Power; they only need 1 each. (And make it 1 Endredux for Clear Mind.)
Psionic Lance is a dud. Take it for concept purposes only. Consider a more practical power as a replacement, such as:
Subdue - 32% more damage than Mental Blast, same cast time. Semi-reliable root. Help keep an AV (which you can't recharge debuff much anyway) from running around and being annoying.
Air Superiority - Almost as much damage as Mental Blast, slightly faster cast time. Reliable knockdown. Smashing instead of psi damage. Juggle a mez/slow-immune target or Elite Boss all day long, plus deal with robot enemies easier. And another place for Kinetic Combat if you're into that.
Afterburner - Faster fly speed between missions. 15% enhanceable defense buff to help get past perceptive mobs. Does not suppress when clicking a glowie. Potential value as a panic button, between Afterburner, Regen Aura, and HA spam, you're really tough to kill.
I was working on making this build but im kind of new to defenders and this was my first shot at a empath/psionic defender, any advice would be awesome I am looking to make him a good healer that can survive well in groups and could kill off the occasional baddie, preferably no purple sets