If you need many voltages simultaneously from a common insulation transformer, voltage multipliers are a good solution. Capacitors with high capacitance are now common and multipliers work well.
Never use half wave rectifier, the DC current in the transformer must be avoided at any cost.
Only use multipliers (with capacive input) or full wave rectifiers and or multipliers.
See the following examples.
http://www.ing.unitn.it/~fontana/Comparing%20Half.pdfThe last one I used for my transmitter, providing 300V, 600V and 1200V. 900V are available and not used.
see how small the board is:
http://amfone.net/Amforum/index.php?action=dlattach;topic=30021.0;attach=30262;imageGiorgio