hehehe you are doing the great astronomers dream
building it from the ground up, and customizing to suite. I like your idea about putting a timer on the side do it like the old days !
As for the 12v timers why dont you get that for a start, saves having to change it all over. you can always get a 240 - 12v set up, ( they are easy to make a bridge rectifyer with a cap to smooth it out. I made one at uni a bit of solder diodes and what not and happy days where had a nice smoothed AC waveform to DC
but get a bit of information on it before you build ... 240 @ 10amps can be hair raising! but at least that way you can just take it anywhere and plug it into what ever power source you want.!
Yay to the amature community!