Help with uprgading to larger tank?

Hello! So I have finally chose to upgrade my tank to a 75g. I'm just not happy with my 55g reef, and want to also focus fish as well as corals. In my 55g I have a lot going on, one yellow tang, 3 clowns, 6 line wrasse, lawnmower blenny, and sand sifting star. And for corals, couple Kenya trees, devils hand, toad stole, Xenia's, few chunks of green star polyps, dying bubble coral, few purple mushrooms, torch coral, frag of frogspawn, purple hammer heads. And about 50lbs of rock. I'm choosing 75g because the aquascape is very important to me and I feel limited in a 55g. So I have a hang off the back filter that's for 55/75g, and its alright, then I have no protein skimmer ( I'm aways told don't get one its not needed, and then get one its needed so I'm stuck in the middle ). I would keep my T5s because they will fit the tank. I was thinking of getting a canister filter but was told that they raise nitrates and the hang of the back is not that bad. So should I get 2 hang of backs for this new tank, and do I need a skimmer. Also I was researching and heard that I cant use my sand I have now, and how the tank will crash etc, and only put new sand in the new tank. The thing is that I need to make the tank switch in the same day because the new tank is going where the old one is. My plan so far is put corals in ten gallon, then fish in another ten gallon tank, then all my rocks in a garbage bag. Once the 55g is broken down I would take it off the stand and put the 75 up. Next scoop my original sand into it, then put as much of my water in the tank ( I realized I'm gonna have to make 25g of premix water to make up for size differnce, so I need to save my buckets for this.) then I would fill he tank halfway, then put in rocks, then more water, then corals and fish, next equipment. I have only been in this hobby for 9 months, so I'm still a noivce when it comes to the chemistry part of this hobby, all of that goes right over my head, but I have been able to maintain a healthy tank with heathly fish and corals, and parameters.