You may want to consider getting a sturdy bin or pond for your Goldfish, Koi and Pleco since all 3 types need very large tanks.
For now ?
Cheap indoor ponds can be made from a sturdy plastic bin or water trough. You can buy or DIY a large filter. YouTube has a ton of DIY pond vids. You can make a filter with a new/clean 5g bucket.
A single Common GF prob needs 30-40g to grow and stay healthy. They can hit 8-12" and live over 20yrs with good care.
Koi hit 18-24" do best in ponds and can live 50-100yrs with good care.
Common Plecos hit 12" and need 125g tanks or bigger to thrive. They can live 25 yrs.
Here is one example
Sent from my iPhone using Tapatalk