I suggest you keep it in the prototype form if you also want to interface it to your laptop. The interfacing will require at least one more IC.
We need to understand exactly what you want and how far the unit will be located from the laptop.
My understanding is that you want to be able to press a key on the laptop and have it advance the counter in the unit as if you pressed the "up" button on the unit. Then press another button to initiate the transmission, ie. to the fire the cracker. I would actually like to have a program do everything for me. I would like to be able to call up a sequence, press enter to initiate it and have the computer change the code of the Tx, fire the Tx then count to the next event and repeat the process.
Incidentally, I'm puzzled as to why you need the counter to be able to count down. I would have thought that you would only need it to count up.
I need down in case some thing doesn't fire and I have to go back. I could just reset and count back up to it but that would take too long.
I'm also puzzled as to why you need the "unit" if you're intending to use the laptop. Why not interface the laptop directly to the Tx? (the laptop can do the counting)
I do intend on using a laptop but I would also like to use the unit seperatly. would it not also be easier to write the program if it only has to do three things; count, up, fire, count... etc.
Then make a PCB once you have it all working.