There's no need 750rwhp (6spd) is well within the capabilities of the oem intake plenum.

Depending upon the turbo you choose and the type of racing you will be doing, increasing the rev limit could be a useful modification.

I am going to be running the Precision 6766 and will be doing road racing and the occasional drag racing.

6spd or auto? For a 6spd in particular, in the 1/4 mile, a higher rev limit will be extremely beneficial.

6spd. What rpm should I set my rev limit at?

Would increasing the rpm limit to 7400-7500 be good to do? I have heard people setting it to 8000rpm but that becomes unreliable any input?

7500 would be fine. At 8000 (with a bone-stock 2jz-gte) you will get (intake-side) valve float at high boost levels. This problem is correctable with aftermarket (stiffer) valve springs.

What would be the better valve springs to get? Is there anything else you would recommend me getting for my 750whp goal? Like an upgraded ignition, alternator, any more engine upgrades, etc..

Double springs are ideal, since they have different harmonics. Here's an option:
http://realstreetperformance.com/sto...-gte-2558.html
Note - this is just an arbitrary internet link. That may not be the best price and I have not done business with that company myself. In other words, please don't take my posting of that link as an endorsement of the supplier - just the product itself.

Should I plan on purchasing the TRD LSD? I see a lot of people with them but was wondering if I should get it or not.

As you increase your horsepower level, the TRD LSD will help you accelerate smoothly and straight forward during wheel spin. With the oem torsen-type lsd, your rear end will tend to pop over to the right when wheel spin hits. Note that for roadracing with good tires, wheel spin isn't usually an issue - so a TRD LSD could actually hurt your lap times, since it can cause some speed to be scrubbed during cornering.

If you roadrace, this may be a better option:
http://www.mvpmotorsports.com/Templa...210&SearchYN=N
Search for part number "Cu LSD168K15"