Alright, How much boost and power(whp) can the block hold?
H23's don't have the old floating bores, so it will help to stay more rigid under higher pressures, but..... it DOES have FRM (Fiber Reinforced Metal) sleeves. I've never heard an exact psi that will cause these to fail, although it sounds like you will be producing some very high pressures. They are rather thin so a great deal of pressure might cause some probs. You might want to look at resleeving.
I ask each because PSI determins the life if rings and such correct?
Compression values will have an impact on the rings... that's part of the reason that you switch to forged pistons (tighter clearances).
While whp will determine life of sleeves/rods?
RPMs & pressure will have a lot to do with the wear of the sleeves and rods. WHP is just a measure of the horsepower after transmission losses.
Also, does this motor come with an LSD, i herd it does but i cant find any info to support this.
Can't say for sure on that one. Would be amazed if it wasn't limited slip.
I would like to boost the motor for 350whp and i plan on upgrading worn parts(ring upgrades?) but keeping the oem rods/pistons and im wandering if this can be done safely/reliably as long as my tuner does a good job. The engine already comes with low compresion
Honestly, you'd be better off ditching the cast slugs and getting some forged ones (if only for the increased durability and clearances). You can probably get away with the stock rods and the stock crank is pretty darn good.