Well here are a few to get you started...
Variables are preceded with a dollar ,e.g. $choice
You can read in a variable with the read command . Labels aren't generally used, rather functions. Others like if tests are phrased slightly differently.
Basically, bash is very like dos/batch scripts but with a little more fluency. That is you can make your script as simple as you wish but with the wealth of options available you can often find that an entire section of a batch script is unnecessary as there is one command or function that will cover it all off. With the fluency you have shown above I doubt it will be a difficult switch.
I recommend checking out The Advanced Bash Scripting Guide. It's all free and online and a will take you from the ground up very quickly...it certainly did for me.
Do come back and ask any questions as you go with your conversion. I'll give you one clue though:rather than labelling and using if tests, consider the case command  |