ok about electrolysis,
Multiple cells's and or plates don't really help, neither does high voltage. Its all about current and the surface area of the plates maximising electron flow.
For a back yard expermeint or lab you would use a drop of acid in reasonably pure water, the drop of acid is to ionise some of the water and allow current to flow in the normally almost non conuctive water.
Your choice of plates is quite important as the electron/ion flow usualy eat your plates.
Industrial grade electrolysis is done on steam with some funky additions like catalyising chemcial and plate setup.
If you can't find waht you are looking for on the interweb(you should be able to tho), try a library, or even uni library.
The electrolysis of water and recombining of h2 and o2 to make water always cost a fair bit of energy , as electrolysyis is not particulaly efficient.
I hope you don't think you will actually make surplus power using your setup, if so read some books on thermodynamic..cause it just does not work that way.
Tho you make some fun hydrogen gas bombs.
Burning just the hydrogen by itself makes a nice fireball.
Mixing the hydrogen and oxygen well before igniting makes quite an explosive combination...for best results place in a plastic conatainer(coke bottle) and ignite from remote location. A long stick is probably not further enough away