Help- Questions for a new tank set up...

Hi folks! Bought a used 75 gallon tank that I'm planning on transferring my
fish, inverts and corals into. I currently have a 46 gallon and a 29 gallon
tank set up that I want to combine into the 75 gallon. Now my
question...Anyone have any suggestions on what the best process would be to
get all of these transferred easily into the 75 gallon? I want to transfer
the rock and sand and everything but am confused how I can do all of this
and yet keep the 2 little tanks running until I get the 75 gallon cycled??
Any suggestions on how anyone has transferred tanks? Also, one last
question. It comes with a hood. I'm looking at maybe getting a retro fit
kit for the lighting. Any suggestions on what kind of lighting to get? ( Or
what not to get?) Also, I want to keep rasing soft corals( Mushrooms,
leather corals, zoanthids etc..) and I have a few clams. What should my
light power be?

Thanks in advance and Happy Holidays,
Susan