what about reactors, and lighting, i feel like i know the least about these things

check out my build thread on my 8' 165 gal tank and see what I did. See if you are looking for the same kind of reef it might help.

http://www.canreef.com/vbulletin/showthread.php?t=60533

Then we will talk to see what you figure you want to do.

Lighting really depends on what you want to keep. I would look at what you really want for you tank, and build around that. What are you most interested in keeping?

well, i not really too picky at the moment, so i think i should start with the easy stuff, i dont really know what corals are easy so feel free to suggest, but for live stock, i want diversity, shrimp, crab, maybe lobster? and course, a pair of clown fish, powder blue tangs and some damsel fish.......?

Watch out for Damsels they can be very aggressive if you want a community tank, the best fish for that would be clowns, regal tang, yellow tang, chromis's, blennies and gogy's. There are other's that are good to but can't think at the moment.

Depending on the crab, but if they get hungry enough, they are known to eat anything. A lobster will eat fish, so if you are looking at getting one, it would be better to get a tank specifically for them. Damsel's can turn into wholly terrors in a hurry, so unless you are getting very aggressive fish to go in with it, you might want to pass on them. Powder blue tangs like to swim, a lot, as most tangs do. A 75 gallon is going to be pretty hard on them. The tangs in the family of the Zebrasoma(yellow tang is an example) or Ctenochaetus would be a much better choice for a 75 gallon system.
As for corals, some easy corals that won't require a lot of light are mushrooms, leathers, paly's, xenia, green star polyps, toadstools, or kenya trees to name a few.

fora community tank jawfish are nice and a pistol shrimp/goby pair can be a lot of fun to watch as well.

how many fish am i going to be able to keep in my 72 gallon if i had round 70 lbs of live rock? and what about dragonfish? what should my salinity be at? can i measure this with a gravity hydrometer? if i get LR from an established aquarium, and throw it in there quick will there be die off? is there any point in buying live sand out of a bag? the trace elements are helpful, and which ones are hurtful? im pretty set on regal tangs, and a pair of clowns, maybe some yellow tangs, what kind of price do these usually go for? what is the best way to introduce new fish to an established tank, i know i know alot of questions

1. depending on the fish you get, you could get more small ones, or a few larger fish
2. I don't know a lot about dragonfish
3. natural salt water is at 1.26. Some people deviate from that.
4. You can use a gravity hydrometer, but they can be known to be quite inaccurate. A refractometer is a much better way to go.
5. there will be some die off, but it is still your best bet.
6. this is a debatable one about sand.
7. a regal tang in that size of tank will start to pace due to the lack of space over time and then you will need to get it to a larger set up. clowns are usually good. what kind are you considering? Some can get very mean. I saw a tomato clown in a tank with a lionfish beat up the lionfish. If you are considering getting more than one tang, make sure you do it all at the same time to lessen the fighting. Prices vary quite a bit, depending on the retailer, or if from a fellow canreefer.
8. It is best to first quarantine new fish so that if they have a disease, all the fish in your tank don't get it. When you are adding a new fish to a tank, you first float the bag in the tank to equalize the temperature, then it is best to drip water in over at least an hour.

I'd stay away from ALL tangs in a tank that small.