Need help on tank upgrade


Happy New Year! I just come back from a week of plant shutdown
and have not read many APD mails yet. I'm planning to replace
my 36" 50gals tank with a 48" 91gals tank in the next few months. 
My problem is that I'm lack of space and would locate the new tank 
on the same spot the 36" is now occupying. I would love to hear any 
suggestion on how I should do it.  I'm very sure I need to break down 
the old tank first. What should I do with the fishes and plants during
this transition? My main worry is for the Kribs as they would fight for 
territory. Should I use back the old gravel?

I'm also thinking of adding the substrate heater this time. I'm
just worried about what would happen when pulling out the plants,
especially the big one. Would this mess up the whole cable setup?

Thanks for any suggestion and input.