Transfering to a 75 from a 55 gal

Hello guys I am getting a 75gal nice setup off Craigslist and am going to transfer the entire content of my 55gal into the 75gal. (gravel, fish, filter+the used media in it, plants, decor etc). Is there anything to watch out for when transferring? I dont want to cause any necessary stress to my fish I just want a nice easy move. (gonna put them in a few 5 gal buckets as I move and I plant to keep most of the water from my 55 and put it into the 75.

Yea thats what im worried about... some of my fish arnt super hardy and I dont want anything to die... is there any preventative measures to take? Im hoping to get the whole 55 gallong+used filter media+used gravel+plants into the new aquarium (hopefully on all the water everyting else will obvi fit idk if ill have enough space to store the water while I drain). So ill essentially be adding 20g of water to my old tank... using this method are there any other steps I can take to prevent any dangerous spikes?

The filter I am using now is actually too big for the 55gal tank... it displaces my hood on top its so large its for a bigger tank but I got it with the tank. On the 75 however I will be running dual filters, one that comes with the tank and the filter from my current tank (unknown filter type but LFS said rated for a 75gal, takes 4 large carbon pads) so the filter fitting wont be a problem, I just was concerned about anything else I wasnt thinking of that could potentially harm my fish