You make perfect sense. My 55 has only been empty a week so the 3 year rule can’t apply. I can’t get rid of my smaller tanks because they house bettas which can’t go together. I have consolidated all of my tanks into a fish room except my 75G and 45G goldfish tanks. The 55G will go in the fish room too.
Wow, it's nice to have a "fish room"...
Did you install any automated water change?
It will be easier for you to change water.
Or get some customized some tanks with holes for connecting hose/pipe directly to the taps, drains..
Some people installed permanent water pipes to their fish tank for supplying fresh water.
For selecting new fish for your 55g, choose carefully the fish that you want. There are many species of fish, inverterbrates which are beautiful and unique.
Take your time to choose.
I'd tried many species of fish (from South America, Africa, Central America, Asia, Australia continents) in the past.
But now I only keep Discus, Furcata Rainbow, Killifish, Lemon Tetras and one Betta in the community tank.
Try to have fish on different levels of the tank(bottom, middle, top) so that your tank won't look so empty.
Schooling fish makes better effect and you can see their interactions and behaviour better.
Also, try to have multiple colours fish.
Red and yellow colours are the most striking.
Blue is a unique colour and it will glow in the dark. My Blue Diamond Discus is absolutely stunning under the dim light.
Green is also a nice colour.
Some Zebra Danios have a thin stripe of flourescent green is also stunning. It wont be nice if the whole body is only flourescent green as its not natural.
My Furcata Rainbows have blue eyes, unique fin shape with yellow tip..
I used to have Neolamprologus Caudopunctatus(from Lake Tanganyika, Africa) which have blue eyes and yellow fins. They are beautiful.
Look through the internets, youtube for ideas.
But sometimes it also depends on availability at your LFS.
To me, I will only select the best available fish cos it's no point to keep some mediocre/ average looking fish as it requires a lot of work to keep the fish...
Marine fish are the most colourful but will require more maintenance plus you need someone to top up water when you are away(1-2weeks) for vacation.
Some may install an automated refill water to maintain the proper salinity as the water will evaporate every few days and increase the salinity.