Hallo!
you must convert AC to DC current, using some absolutely not pricey stuff - it contain diode (actually i dont know exactly what it is and its name in english) but in any electronic parts shop you can ask for something like this. note that this will be NOT a transformer. a transformer will be less effective, will generate more heat from electricity used.

also, there must be at least 50 cells in electrolyser, to get about ~2Volts for each cell. In my country, the problem are bigger - ordinary current is 220V (50hz ac) so if wanted to build an enlectrolyser, there must be at least 80-90 cells, and of curse, additionally this simply and cheap device which converts AC to DC. some other member will know better - about this device needed.

about plexiglass - i used it, because i saw Jetijs hho generator, also made from plexiglass, and this material is known to be KOH and electrolysis proof, strong enough, and very easy glued, if parts are in correct sizes.