You really don't need new pushrods with the LT4 springs, they aren't stiff enough and the rockers in the kit are SA. If you were to replace them and no changes have been made to the heads (milling, valve seats...) you should be fine with stock replacements, but it is always better to measure.
You will be fine with stock injectors on that cam, as for the other stuff it will add a few hp here or there, no need to buy it all at once.
Yep its slow.
Making the world a warmer place one gallon at a time.