Tank upgrade questions

My brother in law wants to give me his 80 gallon with 30 gallon sump for free!! Way better than my 45 with no sump. It doesnt leak, pump works, nice stand, all the plumbing already done. I however would like to do the upgrade without killing anything or having to start all over. I'm 5 months in to this process and I really do not want to see it go belly up. The lights I have are good enough the new tank is the same length and height just twice as wide. So questions:

1. I have 50 lbs of live rock, is that enough? I really don't want to buy more if I don't have too (SO EXPENSIVE):bawling:.
2. Is there a specific process to changing over, I'm guessing it's like a really stressful water change?
3. I know I will need a bigger protein skimmer, and more power heads, anything else?
4. Use the old sand?
5. Best suggestions for a sump setup? I don't know how many chambers it is.
6. What else am I missing?

Again being that the tank is relatively new I think that now would be the time to change it, but I'm just guessing. I would really like to get rid of the filter and canister and would love to have twice as much tank, but not at the cost of losing what I have now. Please let your experience and knowledge guide me in the ways of the marine tank upgrade.


SPECS(Current)
45 gallon tank, aqua clear 110 filter (500g/hr, sponge, 3lbs of LR), Hydor 450 external canister (Bio balls), Aquatic Life Mini Skimmer, 50 lbs LR, Live sand substrate, 2x 650gph power heads, Fluval T5HO quadx39W. SPS frags x2, 1 mushroom and 1 paly. 1 Coral Beauty and 1 Ocellaris Clownfish, and clean up crew.