DC power supply questions

Hi all, I'm trying to assemble an unregulated DC power supply that will
run at about 135V and 3kW total. The bridge rectifier and capacitors
are no big deal to source but I'm having a problem finding a transformer
big enough. A couple questions:

Can I use a variac transformer if it's rated to 3kW? Searching the
archives tends to say that this is *not* an isolation transformer and so
I should add one of those for safety. Would a 3kW variac + 3kW
isolation transformer do the job? Should I put the isolation
transformer on the supply side or the load side of the variac? Are most
240->120V step-down transformers isolation transformers? Am I going to
get bad voltage fluctuations because of the nature of the variac?
Should I skip all this and keep trying to find that mystical 90VAC 3kW
toroidal transformer under $300?

Are there any special problems with running multiple capacitors in
parallel to get the desired capacitance?

Thanks, this group is amazing.
Michael