Okay, my first recommendation would be to narrow down what you're aiming for. You said you're looking for regeneration and defense. What kind of defense? Which type or vector? For example, if you decided to go for smashing/lethal defense, you could take Scorpion Shield. If you wanted ranged defense, slotting a lot of Thunderstrikes would be the way to go.
I personally wouldn't build for +regen for two reasons. One, Corruptors have relatively low hp so you're never going to get a great deal of hp/sec. Secondly, and more importantly, you've got Twilight Grasp. It's a great heal. It heals a lot, recharges fast and is a debuff to boot. It'll be more than enough to keep your green bar healthy.
Looking at your build, you've got defense in the teens to all three positions and all types and just over 20% for energy/negative and ranged running Shadowfall. I'd recommend you choose a type or vector and get it to 32% or so. That means a single purple inspiration will take you to the softcap (link as to why its such a good goal).
There's stuff I'd change about the rest of the build because its a little all over the place at the minute, but the main stuff is as follows: I'd drop or really reconsider the Leadership pool. Fire/Dark is quite an end hog and Assault/Tactics provide very little benefit for the endurance cost for you. Assault is also overslotted, I'd put 1-2 level 50 end rdx IOs in it if you really want it.
The Dark Servant would really benefit from some accuracy. Tactics will help him, but its better to slot him properly. If you want a dark themed epic, I'd go with Dark Mastery over Soul Mastery. Power Boost provides fairly little benefit to Fire/Dark, Patron Pets are pretty much all terrible and the Dark pool has several awesome powers. Like Soul Drain, to turbocharge your damage and Dark Consumption for your end bar.
Take a look at the Dark Miasma guide in my sig. I've got my build in there if you want to check it out. Once you know what you're aiming for, I can be more specific with your build.
My recommendation for a Fire/Dark would be lots of recharge and recovery, moderate defense (32% to a given type/vector).
As for the market stuff, read the market forum. Lots of great information in there and they're very willing to help people willing to learn. But the basic idea is this: buy low, sell high. I realize that sounds like facile advice, but that really is the core of it.
Look up builds on the forums, see what sets are used a lot. Look at your own builds, see what sets you use a lot. This will give you a pretty good idea of the demand for a given set. Then check out the market. See how much the pieces of the set sell for, say Doctored Wounds. That's a popular set because it goes all the way up to 50, its a heal set and almost everyone has a heal of some kind and it provides 5% recharge. Everyone loves recharge.
So you look at how much pieces have been selling for, work out a rough average and put in a lowball bid. Putting in bids slightly above the lowest sold value and selling for slightly below the highest sold values is a good way to go. Crafting stuff up is also a very good way to make money. The recipe + salvage costs is often much less than what the crafted IO sells for. You can pick up lots of desirable recipes for little, buy the salvage (or get it using ticket rolls), craft it up and sell it for a healthy profit.
Hope that helps. So yeah, take a look at my guide if you want, decide on a focus for your build and I can try to help out some more 
Support Guides for all Corruptor secondaries and Fortunatas
The Melee Teaming Guide for Melee Mans
The Melee Teaming Guide for Melee Mans
What if you could build a tank with most of the resistance of a fire tank?
More -to hit than a Dark tank/scrapper/brute.
More damage than any tank?
You can and that's why I have instead built my Fire/Dark based on Resistance.
Let me explain my thinking:
I considered what effects do the Dark powers actually cause?
1. -To Hit
2. Slows
3. Disorient
4. Fear
5. Quick Heal
6. Resistance
So if as Patron powers I choose:
Dark Embrace 41 Toggle: Self +Resistance(Smash, Lethal, Negative, Toxic)
Power Boost 44 Self +Special
Summon Mistress 47 Summon Fortunata Mistress: Ranged Moderate Damage(Psionic)
Then looking through the IO sets I found numerous ways to increase my Resistance/Defense to mezzing. My idea and it has worked amazingly well was by using high Resistance, some Defense and allowing my Heal and -to hits to act as armor for me - I could become a tank.
It worked. I do get mezzed occasionally but it is extremely rare and when I do I count to 3 and heal from the mezzing offender thereby dropping his to hit so I don't get mezzed again.
In gameplay:
Approach a group using Superspeed with Shadowfall (resistance) and Dark Embrace (more resistance), "paint" a boss or mezzer with Darkest Night High (-to hit).
Turn a corner drop tarpatch and once they hit the patch Fearsome stare (-to hit), Howling Twilight (stun + -to hit + slow and terror in Lt and Boss)
Fireball, Fire Breath and Rain of Fire and let the flames roar!
You have them slowed, minions stunned, -to hit through the floor, you have a 30% -resistance on your foes and stuff feared. I personally added Provoke with a chance to stun so that I can possibly stun that boss with a word
I built as a tank and I have so much more damage and other tools that it can be amazing.
The dark servant's melee range -tohit at base 30% debuff, pet twilight grasp and dark controls are gravy on your meal of mobs.
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
Hey! I am new too Mids and the Forums (NOT to CoH) and just recently made a Fire/Dark corruptor. I got kinda bored, so I made him a build using Mids! Here it is:
http://www.cohplanner.com/mids/downl...A8FE013046DA4B
EDIT: Sorry, I didnt really specify what I wanted to do, although it's pretty obvious. I would like to make a Fire/Dark Corruptor with great regeneration and defence. I think I did pretty good for my First build though...not sure. I do have a lvl 50 Fire/MM Blaster, but I just recently got him there and haven't IOd him yet, and I dont plan on doing so, I want to do something different. The Fire/MM was extremely unplanned and I wasted my money on farms.
PS: I've heard a lot of people say they can make 100 mil + in one day...how do you make so much money? I have no luck with the market, even if I DO get something good from a tix golden roll. I want to actually be able to AFFORD this build rather than just feel good that I can make one lol.
Thanks!