Looks like a barely started saltwater tank.
Maintenance depends on livestock, how much and how often you feed, filtration, and a host of other variables. Do you want fish only or plan on corals as well?
Saltwater is not a cheap hobby!
Expect to do 10-20% water changes weekly and/or bi-weekly (saltwater). And daily water top offs (rodi
fresh water). Cost will depend on if you purchase pre-mixed saltwater from LFS
or mix your own and if you purchase rodi
or make your own with rodi
Equipment wise i can see you have a sump, protein skimmer, and what looks like maybe a uv
sterilizer(the white PVC