The reason most people don't have the ideal fish room is cost, I did all the work I could myself but you still need tradesmen for some things.
A drain connected to the sewer.$1000.00
Electrical work, including an rcd on your main switch board(you will have spills)I had a pipe burst, it sprayed my power board outside my fish room with LTs of water, I was right there when it happened >>> I would be dead if I didn't have one!
Installation of power to my shed and fish room cost over a grand @ mates rates > worth every penny.
Plumbing of the tanks I did myself, I even got trade prices for the pvc and it still cost $1000's just for the pvc.
If you need a lot of new tanks this can be expensive too, find a glassier who can help. I think you have one close by that posts here(nzka).
You may have to compromise, spend the money on essentials and then on things that make working in there convenient.
A tank syphon system like Phil's is not ideal but it does work for him, you may find it does not work for you in all cases.
As you formulate your plans - lay out, stand in your shed and visualise not only what it would look like but how things will work > trouble shoot before you build.
If you want a great fish room, you may have to go on holiday and visit many people with fish rooms good and bad > we learn form our mistakes allow others mistakes to help you(I know that's what your doing here but there's nothing like seeing it and poking you head under and over to see for yourself, getting people to show you how they did things out side your knowledge).
All my ideas I got from looking at 5 fish rooms(4 were local, lucky)and still I would change things if I could do it again, small things that allows improvisation to work better.
You may find things you want to do - there is no equipment for(plumbing mainly), making things for yourself - improvising works wonders, there are always ways to make ideas come to life.