Technically you don’t have to .. but those transition numbers indicate when those eips come into play. If you are going to use any of the features then it makes sense to set them to kick in from the beginning.
You also don’t need the dao transition since in your private blockchain the dao never happened
You can not change the gas price of EVM instructions without hacking the core and totally forking off to a new client. This is true for both Geth and Parity.
If the gas limits are not sufficient for you, you can just increase the following configuration options for Parity:
--gas-floor-target GAS Amount of gas per block to target when sealing a new
keorn's chain spec converter is a usefull tool to convert geth chain specs, but I do not know of any tool working the other way around.
It's best to start with a working set of genesis files and chain specs for both clients. Since this question keeps coming up, I created a working chainspec for both clients:
git clone https://github.com/5chdn/crossclient-...