L-pad (and insulated jacks) questions

[Roobin]

Hey guys,

Recently got myself a nice lil' Valve Junior Combo. But, it's still too loud for me even before I push it into overdrive. Thus, I'm going for a simple L-pad, as per Bancika's design on his site. I'm gonna use a rotary switch to choose different resistors. Heres some questions:

1) Using a metal enclosure, do I have to insulate both jacks? (ie so that the ive from the speaker doesn't connect to ground)

2) What dB reductions would you recommend? Seeing as there are only 6 (2 pole, 6 way) i'm guessing a range from -3 to about -24 would be most useful. (well maybe not -3dB) BTW I've got a bypass switch, so no need to worry about 0dB.

3) With the bypass switch, do I want make before break (since this means that there is no time when the transformer has no load) or break before make?

Thanks for all your help!